I recently serviced my dual air Rebas and adjusted the travel,by rmeoving a spacer.

All seemed well at first but since noticed that they seemed to be losing a little air from the negative chamber.

Negative air pressure drops by about 20psi,when left overnight,if you leave it longer the negative air leaks and appear to extend the fork travel a little,as positive side seem to be maintaining pressure.I noticed this when I noticed that I needed less pressure to achieve the same sag,though I guess the extra travel will have as much as an effect on this?

I have stripped them down again today,the inside of the air chamber is spotless and free from scratches,and the o rings look superfiically OK.

From the symptoms above,I guess, it is most likely to be a slightly leaky seal between the postive and negative chamber,that is faulty thus allowing air to pass from the negative side to the positive side.

I have ordered a seal kit form TFT anyway ,which I will fit tomorrow,but if a seal is faulty would it be obvious,when inspected visually?

Any other possibilities,or do you reckon new o rings will cure it?

Got to ask the obvious question: you sure this 20psi drop isn't just from air in the negative chamber filling the pump as you attach it? Mine -ve chamber drops 20psi after re-attaching pump.

It didn`t drop by so much previously,and fork seems to extend a little when left……..

It may have been leaking around the o ring due to wear on the o ring caused by a lack of lubrication, I suspect it won't be visible to the naked eye. When I last had mine serviced I was told to drop pressures on both the +ve and -ve sides as this reduces the stress on the o ring. I think I was running about 20-30psi less than the rockshox chart indicated.

do you have a small amount of oil in the air chambers? I don't think they seal properly unless you do

Yes little bit of oil (5ml)in the chambers.
Think I`ll just fit the new o rings and see how I go.