I agree with Erik. These are small value decoupling caps. So for those unfamiliar with the amp here are some images and schematic clips:
This is my beloved 332. The caps in question lay horizontally just beneath the top cover.https://drive.google.com/open?id=0B0yvjhlC62G7SHVJczc2ZUV2OGs
Here is a example of the schematic. The two circled caps are on the POS-VCC rail. The other two are on the NEG-VCC rail.https://drive.google.com/open?id=0B0yvjhlC62G7RGVBdkZlcElmTGM
I borrowed the following picture from Google images. The two voltage gain boards can be seen here. The meat and potatoes, heat producing current gain boards, are sitting beneath in a vertical position. All the heat rises and makes the area around the voltage gain boards quite toasty. The caps in question are the bright yellow axial devices. They are physically large for such small value caps.http://brainlubeonline.com/mlrepair/IMG_1020.jpg
So the real reason I started this thread is not because I was looking for an esoteric cap to put there. These caps are a focal point for ML and they are old. My concern was the temperature. A PP cap (the type originally used) should perform better in heat than an equivalent ceramic. I say "should" but I am not an engineer. I am only using information that I have seen proven in videos that compare different capacitor types.
The second reason is that if you tap on a ceramic cap it will induce a small voltage. This can be seen on an oscilloscope. These decouplers are tied to rails that small audio path transistors use. Couldn't induced spikes of noise make its way back to the audio path? Granted these tiny ceramics do not have much surface area. A larger ceramic would have higher probability of inducing vibration related noise but to me 8 tiny caps producing 8 tiny spikes adds up to 1 mess. An amp of this size will always be on the floor, subject to whatever vibration the surrounding loudspeakers produce.
I am not saying the ceramic option is not the way to go. I am sure the ML engineers had to put some level of thought into this but in a world where folks have power cables elevated from the floor and where using cryo-frozen power outlets, wooden knobs etc is the norm in the realm of the esoteric, it seems odd that ML would take this route. I personally do not subscribe to most of the insanity but it does not mean I do not read some of the articles describing the latest "sound salvation" gadgets. I want to learn from them, as there could be some sane measurable information in there that I could use one day.