+1 for Chambers. Knibbs usually has parts also.
75 didn't change much through its life. All the earlier ones I've had / seen had the same trigger units. I'm not too familiar with the later 75 T01 but know the rear sight has a different fitment.
I'm reasonably certain-via Robin C on here- that any diopter made to fit 11mm Dovetails fit earlier 75s with very slight and easy modification. Robin is the man to ask.
No way to check if seals are on the road out without firing the gun as far as I know.