Hi Guy,
yes I've now fitted leather washers to both my Ospreys but it involves cutting the piston head back, so a one-way mod. They shoot well at 9ft lb with springs I can easily fit without a compressor. I would say the original plastic rings give a very smooth quiet action, but they wear out after a while and I got fed up with yearly replacement ( I used one a lot....) I also shortened both barrels to 14" and accuracy seems good for target / plinking up to 30yds but neither the modified carbine or the original version will equal a TX200 at 50yds. Having said that I sold the TX because I prefer the slimness and easy loading of the Webleys.

I did try a HW30 piston washer in one Evert, it worked well but the action soon got harsh because the seal was damaged by small scratches or machining marks at the end of the cylinder. These might have been unique to my Osprey but it's worth doing some careful polishing if possible.

Cheers
torrens