I recently put a gearbox from a 1750 in my 10503 Duetto. It's never been apart, shifts great, but has an audible harmonic type rattle at the shifting tower that can change (and sometimes disappear) with pressure on the shift lever. Not a worry but I'm curious. My guess is that the reorientation of the convex baffle washers is the cause but I noticed in the 1750 parts book that the the venting blocks show shims and no shims were on this box. Anybody familiar with this issue?