You may not have the header tube inserted far enought into the muffler.

Loosen the holding screw and twist the muffler back and forth pushing the tube in as far as it will go, then re-tighten.

You can use high temp sealant to make a better seal, but unless you see gobs of smoke coming out of the tube, this isn't your problem.

Try to angle the muffler exit DOWN to help with the oil issue....


BTW: one thing you should check ASAP which many miss.

The pressure nipple on the muffler of ALL glow engines can and will get full of crud from time to time.

I don't know how many engine problems I've cured for people by walking up, pulling off their pressure line, sticking a small allen wrench in, reconnecting and telling them to fire up their plane again...

You may not feel resistance to inserting something to clean out the crud, but it can be there never the less, preventing your fuel tank from pressurizing properly and killing transition performance.