Re: Master Clock contact spark quenching
As it's now 2021 you could consider using a solid state relay - silent, should last for ever, no inductive kick to make any arcs across the clock contacts.
RS sell 'em in 5s which is inconvenient unless you have a use for the other 4, or could share a pack. There are probably other suppliers - in fact eBay:
have them at double the price in ones though.