When letting air out of my forks (revelations 2011) when according to the tech manual only grease is used to lubricate the air spring.

They will probably have a little bit of oil in to keep the o rings lubed as they slide up and down. Unless its pouring out its quite normal.

Grease becomes oil in use totally normal if it’s super dirty then it time for a service. They come with a heavy o-ring grease on the seals but a little red rum on the top of the postive air piston seal head makes them super slick.

Air chambers have oil in them to lube the seals. Simples.

So when i service the air spring, although the tech manual states to only use grease, should i use oil aswell and if so how much ??

I’d put a little oil in. All forks I’ve worked on come with oil in the air chambers, and it will work better than grease imo.

As for how much, it’s up to you. You can fine tune your spring rate with oil in the chamber if you like.

Just a dribble to keep it lubricated. A bit more will reduce the volume and make the spring rate more rising (although though too much will limit your travel of course).