Old, leaky Umarex P99 - Repair ideas?

[Airsoft J2]

I've just picked up my 12 year old Umarex P99 (fixed slide) gas pistol for the first time in a long time and have found (perhaps not unreasonably) that one of the magazines is very leaky and the other is losing pressure more gradually.

Unfortunately, I can't find them for sale any more so I'm hoping to fix it rather than replace the pistol - any suggestions beyond replacing and greasing all of the seals?

 

[Rock-climby-Dave]

all the valves are reparable with time and the right O-rings.

good starting place is a £4-5 bottle of abbey maintenance gas. Usually sorts out slight leaks.

 

[Airsoft J2]

Cheers Dave, sorry for the tardy response. I'll start with some maintenance gas and lube and see where I get to.