Hello again.
Re the seal behind the damper, I've just remembered that after making up one myself I managed to find a factory replacement seal which I never fitted (I think it's that seal anyway...). It is made of quite hard plastic and is 26mm in diameter, has a central hole 18mm in diameter, and is 2mm thick. Hope that helps.
I was advised to use red transmission oil in the damper and I just bought the first one I came across. It seems to work a treat.
I did order the steel piston seal from Anschutz. I think it was actually for an LG380 but they are identical to the one on the An250.
Looking through my spares box I discovered that I do have one spare pair of damper seals which I will send to you (free) if you let me have your address by PM.