What I don't understand is: Are they really a fabricating company? Or do they just buy from someone and resell? Any fabricating company worth half their weight in salt would know the proper way to fix that, and it wouldn't be by enlarging the offending hole. You weld up your mistake and re-machine.
The problem is, if they're dumb enough to mis-drill it in the first place, even dumber to suggest wallowing the hole even bigger till it fits, are they going to be smart enough now to fix it correctly. I highly doubt it.
Like was mentioned earlier, I wonder what else they don't know about the flywheel manufacturing business.
Tom