Garrard RC75 record changer (Woodley RG5)

I offer this as a restoration project. It worked OK when I copied my 78/45 rpm records to tape and has since sat in a cupboard. But when I checked somehow the mechanism has got out of synch. There is no damage, nothing broken or bent. I suspect that the geared cam that actuates the record changing and switch-off is misplaced from it's correct start position - for example it will play a stack of records but then switches off before the tone arm has fully returned to it's support.
I replaced the original tone arm with a lightweight arm made out of CFRP and fitted with a standard cartridge mount.