the army L85 is a G&G clone, i bought a G&G 2nd hand so i have a little experience.
From what i know, there is 2 issues with the gun.
1)The first one is caused by the PSG1 piston/cylinder, if yours has one, it may be shooting wayy over 350fps, and from my experience it was a bugger to get below 350 for me.
There is ways round this, you could do the conversion, whereby you swap the sector gear for a v2/3 item, fit a standard piston with a 10mm spacer between the piston and the piston head and a standard AEG spring. doing this you will lose the pre-cocking though, unless you keep the old sector gear and remove the first 2 teeth off it.
my gun had a really bad conversion done, so i re-built my gun. that said i have a new complete gear box on order (see below), as i want to try out the pre-cocking etc.
2) the blow back function. This will at some point break, as how it works is by having plastic prongs going into the spring, and attaching to the fake bolt. most people just disable it, as if it breaks .... well there are 1 or 2 horror stories about jammed and stripped pistons.
now the good news ... the gear box is really good and strong, it has a spring release leaver that releases the anti reverse latch, and it has a quick change top end facility (so you could swap the top end for different FPS sites etc). but best of all, you can get a whole new gear box off ebay for less then £60! http://www.ebay.co.uk/itm/Original-L85-R85-Gearbox-for-G-G-L85-AFV-L85A2-ARMY-R85-R85A1-Airsoft-AEG-/201203795357?pt=UK_Sporting_Goods_Paintballing&hash=item2ed8ae459d
Don't let this put you off though, as there isn't a perfect L85 out there, they all have there issues.
Ares have had a bad reputation for gears being made out of pressed cheese.
Avoid STAR as they apparently have plastic gear boxes.
ICS can have feed issues (a mate off mine had this with his brand new gun, soo much that he took it back), and at some point may strip its piston (see airsoft Ed's review).