So, yesterday I was just about to remove the piston and replace the seal. Before I did so, I thought I'd just try it out to see how it was performing. The answer was "very well". I had about 15-20 shots with it and all was good. So, obviously, working the Pellgun Oil through had worked nicely. Apart from one shot at the end where compression was low.

So, before I replaced that seal I thought, "why not give it a go with the 30wt. oil and a little moly". Applied a couple of drops of oil to the piston and held vertically and then applied a small amount of moly paste to the piston body and applied another drop of oil to make a runny black "moly oil". Whilst working it through the pump, I noticed that at certain positions of the pump stroke, with the pistol held upside down you can see and gain access to the air inlet hole on the pump tube. I thought this would be a better way of getting the oil where it was most needed, ahead of the piston. Applied one drop of oil and held pistol upside down for a while to allow it to get into the tube properly. Then worked it a few times and wiped any bits of excess oil off.

Wow! Smoother AND compression seems much fuller and priming effort now much higher and more consistent. Had about another 25-30 shots and seems perfect. I'll give it another go very soon and see if this restored performance remains but, for now, looking good. And I still have the seal ready to fit as and when needed.

Thanks again for your input chaps.