Saw still doesn't go back to idle

Not to long ago I posted about my 970 not going back to idle after the throttle/trigger was released. Thought it might have been the way the idle adjustment was set and that the spring for the screw might be weak. I was going into town today and took my saw to my Stihl dealer - liitle hole in the wall, but a good bunch of guys. As would be my luck, the saw ran properly while I was there, but the mechanic did notice a trace of fuel leaking from where the tank vent might/should be. He said that fuel leak was probably my problem, that the tank vent or one of the fuel lines was faulty and air was in the system causing the saw to sometimes not come down to idle. He would have looked into it right there, but being a Stihl dealership, didn't have the parts. When I came home and was putting up the saw, I could here a slight "hissing" or similar sound coming from where the fuel was leaking.
So, does this "air leak" sound like what could be the problem? If so, then I'll have to find a IPL for my saw (Olympyk 970) and maybe a shop manual so I can try and fix the "leak". So far my only work done to a saw is changing a carb on my 260, minor muffler mod on the 260, and fixing the chain tensioner assemby on the 260, and other minor stuff. I'm no saw mechanic, but with a little help from manuals and people and a liitle common sense, I can get by mechanically. So should I attempt this fix myself? or have a saw mechanic do it? Without a manual, I'm not quite sure how to remove the fuel tank assembly. Any help is appreciated.

Kevin