Hey guys. I haven't been on for awhile. Anyways, parts compatible with the famas are most V2 gearbox parts EXCEPT the tappet plate, selector switch, electrical stuff, etc. The gears, bushings, springs, piston (half tooth), and piston head are compatible. Cylinder heads are compatible if you put a little bit of electric tape around it so they don't slide around in there.
The only problems with the V1 gearboxes is that it can hold up to an M110, and i have heard rumors of M120's and m130's in a version 1 gearbox. I personally dont want to chance my gearbox breaking, so i only put an m100 in it. the other problem is the motor. The motor is a high speed motor but cannot pull large springs. That is another contributing factor to only being able to use low powered springs. Other than that it's just a matter of finding parts.
Go to trinityairsoft.com and click on "famas" under the "parts specific" menu thing on the left side of teh screen. then click on the famas that you want, V1 or SV, then all the compatible parts will come up. Trinity actually has quite a few parts on there.
As for it actually breaking, mine broke a couple of months ago for teh first time in 2 years. and that is after all kinds of wear and tear, dirt, a whole ton of custom modding, etc.