If you gun is leaking where the needle enters the air cap section, this is most likely the culprit. Solvents get in and attack the seal.
Anest Iwata Needle Cartridge Packing 93765610 Needle valve packing set KIWAMI-1
Anest Iwata Needle Cartridge Packing 93810620 valve set KIWAMI4 WIDER4 WS-400
Iwata Needle Cartridge Packing for LPH80 93940890
Iwata Needle Cartridge Packing 93765610