Cheers, Dave. That analysis makes sense. There was a RWS 45 for sale up here recently which had been converted to synthetic and was running a Titan spring. I was very tempted with that one but I did consider it a possible recipe for running hot.
When I stripped my .177 O45 is expected to see some modifications because the thing is so sweet. But it was still running leather with the usual piston sleeve and spring guide. The trigger was modified by the previous owner, though.
I think there is a synthetic seal marketed in Germany for the 45 as well. I'll have a wee search for it.