my first M14 I kept running for tens of thousands of shots with home brewn fixes for problems, the gun itself was insanely accurate but had some issues like jamming caused but the architecture of the bolt and nozzle, and theres nothing you can do to fix that, its just the design (the nozzle is very long and when extended the support only touches the very base, so especially if conditions caused the gas pressure to be a bit high, the nozzle can be pushed upwards so it jams at an angle, doesnt happen alot but its pretty dang annoying)
the main upgrade for the we M14, the steel trigger box, is insanely expensive, but right now on the forums theres a smoking deal
http://airsoftcanada.com/showthread.php?t=161237
If I didnt already have a RAtech M14 socom with a USGI walnut stock I'd have bought this weeks ago
FWIW Id get a regular versdion not an EBR, an extra $500 for a huge ugly bulky stock that in all likelyhood is crappily made anyways? no thanks