Vac Renaissance 30/30 -- difference between original Mk2 and Mk3?

Can anyone explain the differences between the original, Mk2 and Mk3 versions of the VAC Renaissance 30/30 amplifier? And how old would the original be at this point? Any age-related concerns at this point with buying a used original 30/30?

Also, I appreciate any comments about the sonic differences between the three versions.

Thanks!