So today, I was trying to start my xcell, and I heard a whistling noise. Turns out, the little disc that has the glowplug on it, has air coming out of it where it meets the engine. So I took it apart, and put it down, and tightened down the heat skink a little tighter (stripped a bolt :-/) and yet air is still getting into the engine right there.

What do I do?

Doesn't sound good There is a chance that you could pull the heat sink and drill and tap for a larger screw. While its apart you could use a straight edge and make sure the 2 surfaces are nice and flat, buy a new washer and then torque the heat sink down properly. If your not sure about working on the engine I think XTM has an exchange program. You might want to get in touch with them direct threw http://www.globalhobby.com Which ever good luck[:-]

I stripped a bolt on the head I put it on a drill press ind drilled the head off the screw thenfilled the small indention with quick steel and re drilled the screw hole it take a little work but it works good as far as the air leak you may need to get new shims

yeah that liquid **** that hardens to steel then ya can tapp it works like a champ...did that ona head bolt on my 1:1 heavy chevy and worked like a champ!!!