Walther Air Guns
i found this interesting post on Network 54. The poster swapped out the stock LGU spring and seal for Vortek parts.
"For about $30 you can get a Vac-seal 25mm piston seal and a HW95 OEM replacement spring (.125" wire X 33 coils) from Vortek. I put this in my .177 and it is as smooth as ever...