Your carb screw story is an example of bad business. If the screw was never removed, it is not the modelers fault if it was sucked in. If it had been removed, then it would be. The screws are distorted after they are installed to prevent them from comming out.

As for total dissasembly of the engine and polishing it, I do not believe any manufacturer would warrenty an engine after that. There are just too many things that can be done incorectly that will cause a failure. Just not cleaning all the grit out good enough can destroy the engine. I would say if you do that, you are going to be on your own.