It's probably a result of silicone/lubricant residue on the hop up and as a result the hop up not working it's magic to it's fullest extent.
As for lubricants the WD-40 would eat at any rubber in the guns. Ttry it one day, seeing it for yourself is the best proof. Go to your local hardware store and buy a few rubber o-rings or something made of rubber and try spraying a bit of WD-40 on it to see what happens.
Anything else would be fine to use WD-40 on (although it's moreso a rust remover and NOT supposed to be used as a standalone lubricant).
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE