Accuracy will be to do with the Hop Up and Barrel. So the best thing to do is get a new HopUp, Bucking, Flat Hop (R-Hop if you can) and a quality tightbore barrel.
The FPS issue may be to do with an airseal issue as its quoted at 340 FPS on Airsoft World website. Maybe try a new air nozzle.
Overall durability of the gun should be to shim and correct the AoE so it keeps going for the future!