They are rare? I thought it was common with Midway boards. I've had sync issues with plenty of non-Midway boards too. It's not a rare issue at all, hence why a sync cleaner is an absolute necessity.Cool man. Also any good SG should already have a sync cleaner. I guess yours was one of the rare midways that have a dirty sync signal.
I don't know the difference between a weird sync and a dirty sync. For me it either works or it doesn't. Sorry I misunderstood.