Probably the glowplug is a little loose or the washer (your "brass ring", which I think is actually copper) leaks. New gloplugs almost always come with a new washer.

It looks like a great little truck. Designed similarly to the much-acclaimed HPI Savage with respect to the chassis vertical plates. Videos of it look promisiing.

Parts are only available from Tower Hobbies, except for general purpose stuff, like glo-plugs.