Hi Roy good to see you on here
I usually put a bit of moly around rear of the piston where you will see pressure marks where it cocks
I also put a single drop of silicon oil around piston washer, although from memory I think the Mercury may run on O rings
I remember buying a new Mercury at "Whaleys" gunshop in North London, it was .177 and accounted for a good few Rabbits, and was considered hi-tech back then, I part exed it for a FWB Sport when they became available a few years later
The Mercury had more power than the Airsporter at the time and was about half the price, £35 I think