I've found 4 instances of a re-used plot device. The plot device is Curly going berserk whenever he hears/sees/smells something.

1. Punch Drunks (1934): Curly goes bonkers every time he hears the song "Pop Goes the Weasel" and starts punching out everything within reach, and only stopping the music will settle him down.

2. Horses' Collars (1935): Curly goes insane whenever he sees a mouse, and only a mouthful of cheese will settle him down. Moe, Larry ... Cheese!

3. Grips, Grunts and Groans (1937): Curly goes nuts whenever he smells "Wild Hyacinth" perfume and only tickling his feet will settle him down.

4. Tassels in the Air (1938): Curly goes crazy every time he sees a tassel, and only rubbing it on his chin will calm him down.

What about the epsiode where Moe is supposedly going thru a nervous breakdown and Curly & Larry take him camping for "therapy". Isn't there at least one other episode where one of 'em is sick and the others take "care" of him? Shemp maybe? Someone jiggle my memory......

Here are three (four if you count the 1955 remake) episodes with Nervous Breakdown as it's plot device. (there may be more, but these had nervous breakdown in the synopsis)

Idiots Deluxe (1945)
Moe has suffered a nervous breakdown, and is advised to “get away from it all”. Larry and Curly take him on an outing in the woods, where they encounter a hungry, car-driving bear.

Pardon My Clutch (1948)/Wham Bam Slam (Remake 1955)
Shemp is having a nervous breakdown and Moe and Larry take him to the country for “peace and quiet”.

Guns A-Poppin’ (1957)
Remake of the previous short Idiots Deluxe, where Moe has suffered a nervous breakdown and Larry and Joe advise him to “get away from it all”.

The Dictator like Hitler plot device was used alot during the 1940's. The first was Moe's personal favorite episode, You Nazty Spy (1940), where Moe is set up as a puppet dictator for a small country wanting to raise money, and decide starting a war is a good way to do it.

2. I'll Never Heil Again (1941), a sequel to You Nazty Spy where the powers-that-be plot the downfall of Moe's puppet government.

3. Back From the Front (1943), where the Stooges try to take over a Nazi ship by disguising themselves as Hitler, Goering and Gobbels.

4. Higher Than a Kite (1943), where the Stooges escape the Nazi's by making them salute a picture of Hilter they carry with them.

5. No Dough, Boys (1944), where the Japanese mistake the Stooges as Nazi spies. (this one is a stretch, since Hitler is not mentioned in the synopsis, and I can't remember if Moe does a Hilter impersonation in the episode, or not)

The plot device of Getting Into the Sultan's Palace is re-used in at least three episodes. The plot device consists of the Stooges pulling up to the palace gate in a sleigh dressed as Santa Claus. The conversation goes:
Guard: Who goes there?
Stooges: Santa Claus.
Guard: There ain't no Santa Claus!
Stooges: Yes there is, and we brought you a present! (they open a sack)
Guard: (peering into the sack) What'd ya get me?
(They whack the guard over the head and he falls into the sack)

Here are the episodes this plot device appears in:
1. Wee Wee Monsieur (1938)
2. Malice in the Palace (1948)/Rumpus in the Harem (Remake 1956)

The Light on an Object plot device shows up in two or three episodes.

The premise is: A hole in a window shade is casting a spot on whatever the Stooge is working on, and they spend a great deal of energy trying to get rid of the spot.

1. Pop Goes the Easel (1935), where an artist is trying to remove the light spot on his painting. The Stooges try to help, but end up ruining the picture.

2. Sing a Song of Six Pants (1947)/Rip, Stitch and Sew (Remake 1953), where Larry is trying to remove the light spot from a pair of pants, and ends up rubbing a hole in them.

3. Up in Daisy’s Penthouse (1953), where Shemp is trying to remove the light spot from a pair of pants he took from daddy Shemp’s closet, and ends up rubbing a hole in them.

The Ridiculous Inheritance Clause plot device surfaces in at least three episodes. This plot device consists of someone inheriting a great fortune, but must be married before a certain time of day before they can collect.

1. In the Sweet Pie and Pie (1941)
Three ladies must get married before midnight to collect their inheritance, and pick on the Stooges to fulfill the need for men.

2. Brideless Groom (1947)/Husbands Beware (Remake 1956)
Shemp has inherited a vast sum from his uncle, but the terms of the will state he must marry before six o'clock in order to inherit.

I've found the Study This Map plot device that's very interesting. It first appeared (I think) in the Moe, Larry and Curly episode I'll Never Heil Again (1941) and was exactly duplicated (probably used the same filmed sequence) in the Moe, Larry and Shemp episode Malice in the Palace (1949). It might also have been used in the 1956 remake Rumpus in the Harem. It featured a map that resembled a man's profile "sort-of" resembling the east coast of Europe. It boasted the countries of "Great Mitten", "Jerkola", the "Hot-Sea" and the "Tot-Sea", "ATisket" and "ATasket", plus many other silly names for the Stooges to muse over.

The plot device of Shoot a Piece of Fruit in Their Mouth shows up in at least two episodes. (I KNOW there are more of these)

1. Pardon My Scotch (1935) where an opera tenor is stopped from singing by the Stooges flipping grapes.

2. Micro-Phonies (1945) where an opera tenor is stopped from singing by the Stooges flipping cherries.

The Get Splashed Through a Porthole device turns up in a few eps.

A stooge approaches a porthole on a ship under direction to look for land, or just to catch a breath of fresh air. After opening the porthole, the stooge gets a faceful of seawater when he tries to look out. He closes the porthole, then gets under it, opens it again and tries to peek out the opening, yet again being splashed. This interaction continues until the stooge gets a faceful of mud.

Some of the episodes this plot device shows up in are:

1. Back From the Front (1943)
2. Dunked in the Deep (1949)/Commotion on the Ocean (Remake 1956)

The plot device Three Watches is a funny gag, and it's used in these two episodes I've found so far:

1. Dutiful But Dumb - (1941)
2. Rhythm and Weep - (1946)

The scene goes something like this:
(Moe wonders what time it is, and a Stooge pulls up his sleeve revealing three wristwatches)
Moe: Say, what's the idea of the three watches?
Stooge: That's how I tell the time. You see, (points at first watch) this watch runs 15 minutes fast every two hours. (points at watch at other end) This watch runs 10 minutes slow every four hours. The watch in the middle is broken, stopped dead at two o'clock.
Moe: Well, what time is it now?
Stooge: (pulls pocket watch from pocket) 3:15 ...

There are variations to this theme. Sometimes the Stooge will continue with, "I add the time from the fast watch to the slow watch and divide by the two in the middle."

I'm pretty sure there are scads of this plot device for the finder to reap.