I'm so sorry to read this. I never met Mark in person, but you always knew that an OSB58 post would be calm, well-reasoned, and pretty much impossible to pull apart!
We probably differed on a few things, but it was always done with such grace that it was impossible to take offence. Plus he was probably right anyway.
I'll really miss him and that ability he had to somehow rise above all of the petty niggles without ever appearing arrogant or dismissive.
An outstandingly intelligent man, and more importantly I think, a true gentleman. I think we're all going to miss him.