Not sure where that came from. S6s are a little more to service than the RV8s, but they need less 'upkeep' as they're newer.
My Griff was 18 years old when I sold it - servicing was a couple of hundred a year but upkeep/maintenance took it closer to £1,000 p.a. Most of the old Griffs, Chimps, etc are needing chassis work if it's not been done already and that can be frighteningly expensive. It'll come to the T-cars too but not yet.