Oooh well, there's a question...
Got the Claud Butler MTB out for a final tweak and clean.
Could not get the gears to index. It has new chain, cassette, cables, mechs and shifters. OK, the FD is original, the RD is new to it...
As I don't yet have quicklink remover, I swapped the Altus RD-M310, by cage dismanling, for an older 7-speed model. No change. After yet more fiddling and swearing, I dug out the original, even older, Acera 7-speed mech. Got it fitted, set limits and...perfect, almost first time*. Which is good on several levels. It's shiny and silver and looks better on the bike than the black Altus mechs. Had to reverse the B screw, but then 1994 mechs didn't envisage messing with 34t sprockets...
It's running 8-speed, which I never expected the Acera mech to cope with at that age, but you live and learn!
Will hopefully deliver it to younger son tomorrow!