My 30's era machine, just gifted to me, sews 12 stitches/inch when the balance wheel dial is on 6. Despite the diagrams on the W1,3,5 user's manual, there is only one adjustment screw port on the head. When I removed the covering screw I encountered an adjustment screw with a screw driver slot so shallow that even a custom-made driver won't turn it. I imagine I could drill the screw and back it out with a left-handed thread extractor drill but I'd like to know if there is an easier (sic) way. Does anyone have experience with this problem?