I also have a Watchco SM300 which is in for servicing. I flicked 2 others in the last few days (2846 / cal501 and a Seamaster 600 manual) so just down to the 2 vintage Seamasters at the moment (I count the Watchco as vintage, I realise some people don't).
The Seamaster 300 1st series was one of the most arduous, yet enjoyable, journeys that I have taken through the vintage Omega universe.
I started with a later version 165.024, which is now long gone, and worked my way backwards!