Original 75

[Graemevw]

On a bit of a whim, I've bought an original 75. I've wanted a spring target rifle for some time, this came up reasonably close so I bought it.
Not sure if I paid too much, but too late now anyway.

I know they can have piston seal issues and this one hadn't been shot in 20 years, but it's had maybe 20nshots though it and seems ok, putting out about 6ftlb so it seems ok for now at least.

I don't really know these though so have a couple of questions.
Is there a good online resource for these I need to binge read?

The questions i have right now are, the rear sight. Seems it has a wheel to loosen it so you can slide it back and fore. It's very tight and won't move. I don't know which was to turn it to loosen it so haven't put full effort into it yet though.
I assume it had a rubber buffer on the cocking lever? There is some sticky remains and there is now a mark on the action. Seems like it probably had a small buffer.
The barrel seems to be shrouded in plastic. Are they all like this?
I thinknive read that they changed thebpuston seal material at some point as they fall apart. Is that true? If so, when? If they did change, how can I date it to find out what seal this has?

It would be nice not to have to strip it but am prepared for the possibility the seals may break down at any time.

Thanks.