I use break clean a lot. Have for years. I'm not paranoid about it, but I don't swim in it either. When I've used it on sewing machines it has been on the older all metal ones that just won't clean up with an easier way or when the gunk is in a place I just can't get to.
Many parts on the modern auto are plastic or rubber too. For instance the break and clutch master cylinders on most new cars and trucks are some kind of plastic. Break cleaner wont touch it. Same with many other under hood parts.
But, these sewing machine parts may be made from some totally different type of plastic. So, there's no sense in taking chances.
As for the gears in that Singer, they may not even be available. I emailed Singer for the cam drive gear on our 538 and they tell me it's not available any more. I can get the gears elsewhere and I will, but who knows how long they will be obtainable.
So far, knock on wood, I've only gotten burned once on a machine from GW and that was really my fault. I didn't see the broken off thread take up lever that was visible in the pics. Every thing else that came to me was pretty much as they described it. Of course I've gone for some of the derelicts and dead machines, and so far I've gotten all of them running and sewing. Now I need to pass some of them along as I'm buried in sewing machines.
Joe