In giving the thread a cursory lurk-over, I'm seeing many mentions of old and long on-hand thermal pastes.
I found out the hard way that most thermal pastes have a 'shelf life'. (Industrially-marketed TIMs have the spec on the datasheet.)
I've watched 2 large tubes (purchased across diff years) of AS Ceramique begin to separate across 7-10 years, and have seen at least 1 tube of MX-4 start to separate after just 3-4 years.
-The Ceramique was only noticed when it became (effectively) impossible to push out of the tube.
-The MX-4 clearly was not coming out homogeneously. I managed to just mush it together with the tip of the tube; it 'worked' but, its physical properties clearly had gone 'out of spec'.
Related: also found out the hard way that RTV/Silicone/GasketMaker too, has a (surprisingly short) shelf life. (especially once opened, even if seemingly well-resealed.)
From researching Thermal Putties, it seems refrigeration (and a properly sealed container) will considerably extend its rated shelf life.
Also ran across similar advice in extending RTV's shelf life.
I'd say that it seems any silicon(e) based/derived suspension/mix/colloid benefits in its 'shelf life' via refrigerating. [There are bound to be exceptions.]
I'll probably be storing future purchases of TIM in the fridge.
of note:
my experiences may be 'outlying cases'. Over the last 2 decades, I've completely changed environments (humidity, temp, weather, etc) thrice. Also, the aforementioned TIMs and Sealants were commonly stored where temperatures swung much more than a climate-controlled office, etc. This alone, regardless of staying within 'labeled storage temperatures' could acceleration aging, separation, etc.
Oh, and IC diamond does cause some scratching, but it does work well. (I wonder how well cheap industrial diamond lapping compound would do as TIM?)
Not too hard to polish out most of the scratches, but I wouldn't want to use it on collectable kit.
