I would have a go at servicing it yourself, clean all the old lube off, spray the spring liberally with motorcycle chain wax (aerosol), leave it for the solvents to evaporate, rub the inside and outside of the piston with Moly GN paste, rub the inside of the cylinder with same, apply some moly grease to the ends of the spring, reassemble, all should be well... Moly GN paste is excellent stuff, you rub it into the surface of the metal as if you were polishing it. It's longer lasting than grease and less prone to cause deiselling. Motorbike chain wax is excellent at dampening spring noise, some guns like a smidgin of moly grease added on top of the chain wax. Webleys sometimes have a plastic spring guide/vibration dampener, it's very rare but I have heard of one case where that had broke, also, after prolonged use, these can wear and the rifle will benefit from a replacement when it's serviced.

I seem to remember hearing that Webley guns are usually just oiled at the factory, that was certainly the case with my Tempest. A bit of cleaning, then a modern lube job, with wax, grease, and paste worked wonders on that pistol... I did the trigger with GN Paste as well which improved that too!

Rob M