Thanks for the insights on my problem Jason and Steven. I've checked some type studies and it appears that my 45 dates somewhere between 1900 and 1915. Its fence rods slide through, not screwed into the main body (1900), it has the cutter bolt and clip, but no adjusting screw on the fence (1915). I've played around with the cutter bolt, its washer and clip. Cleaned all those, they were in good shape before cleaning, applied some wax as a lubricant – all to no improvement. A bit more fiddling, has suggested to me that only light tightening of the cutter bolt should be used; I'd definitely been cranking down on it too much.