My old Singer, a 328K only requires grease for the gears, and I suspect, though I don't really know for sure, that my 403A is the same way -- I'll let my son check up on that. In the meantime, I am keeping them both well oiled (but not excessively). I also try very hard to keep the lint cleaned out of them -- that's one thing for sure. I've seen some of the machines that came into the shop where my son worked. The machines were actually packed full to the extreme, and then the women that brought them in just couldn't understand what was wrong! LOL! I'm surprised that some of them didn't totally burn up. Do that too often, and they will burn up! I try to clean the old grease out of the gears before putting more in them -- just my opinion, but I think that makes sense!
Jeanette