0
Listen, just because they have tools doesn't make them mechanics.
If they have you filing down pistons and heads based on whether or not a fingernail catches the burr, well son, you should consider that.
The only proper is to diagnose the cause, repair that and replace damaged parts with new, previously-undamaged parts along with a proper build.
Then again, the flipside to that is, hack away my friend. Let us know how soon before it explodes again.
Ever ask these buddies of yours WHY they're doing top ends "somewhat often"?