ORIGINAL: SMOKEFAN
Is the head loose or glowplug loose? Theres not really a head gasket its more like a shim to adjust compression that seal to the top of the piston sleeve
If there is oil or fuel coming from between the head and the sleeve, the head is loose most likely. The machining is often good enough to get a good seal without a head shim in it. If it were me, I'd pull the head off, clean the screws and screw holes with carb cleaner or some kind of solvent that'll break oil down. clean it up good, blue locktite the head screws and torque in an X pattern.
If you dont use blue locktite, you run a high risk of the screws coming loose again.
p.s. Anpacmn - I see you're from Cloquet, MN. I'm down in Cottage Grove. Good to see another Minnesotan R/C'er here.