I will have a booth open at the swap meet. It will be $10 for a walk-through diagnostic. I will remove debris, clean nozzles and hop area, pull motors and examine for damage. If I spot bad part I'll make. List and recommend the part - if it needs to have the gear box opened: I'll go in and clear that out and grease that for an extra $5.
My strongest recomendation if the gun is a year old , the barel is clean, the bucking is intact and functional, and the gun is shooting slower disappointing speeds. Don't waste your time swapping small parts out. Go buy a rear / front wired, complete Jg-CA-Etc ($50-75) gear box and put it in. I can do that for you if you want as component level repair swap for the $10 fee of a cleaning/diagnostic. Airsoft GI .com has them. That should last you a long time.
Don't try to dig a tick out of his game.... if they won't call a hit, stop and go fight another who will.