I'm wondering whether the piston rings might be worn or something - it's quite an old thing. That said, even though my pressure was dropping, the tools were still running and I don't have anything so "mission critical" that I need a permanent ai supply - it's really hobby stuff.
Having never used air tools before, I do like the way you can swap between them so easily - no need for several power cords for the Dremel, Drill etc. and the fact that working in the rain doesn't pose a problem (obviously they might rust after a while, but you're not going to get problems with electronics not working) - it's nice to be able just to use the air gun to blow swarf/rust/dust etc. out of the way - my engine bay looks cleaner already!! I also feel that if you try to apply too much torque to, say, the die grinder, and it stops, the tool isn't going to be damaged like one driven by an electric motor... probably
Only annoying thing is that I can't get my car close enough to blow the tyres up!!