My Bulldog often has a little smear of oil on the air tube around where different pieces go together, only shows up when pressure is low. I'm guessing that the o rings are not fully sealing until there is some pressure pushing on them. Mine leaks no air after months of sitting even with this "problem". I wouldn't worry about it unless you are seeing a pressure loss after several days.Also remember that the pressure will change after you pump it up and let it sit. From empty it will change more than a top off because of the amount of heat you put into the process of compressing the gas. I'm seeing around 100 PSI drop on my Bulldog (340cc) after a fill from empty (just last night). Similar on my Kral with a 500cc bottle.