Just to say that I took the plunge and contacted Mark and made arrangements for him to come and give my Opti it's annual service today.
He arrived early, made a very professional job of servicing the Opti, and didn't even complain about the tea!
Mark used all genuine parts, has the laptop and diagnostic kit required to check out the outboard properly, and due to his experience and official setup, the service has maintained the Mariner 5-year warranty.
Even better, Mark even made time to service my aux (4hp 2-stroke Mariner) so now I am absolutely ready to go fishing!
I can therefore reccomend as a very professional and thoroughly nice chap.