why is my airfilter ful of oil ?

The bubbling could be due to excess blow by past the rings. The loose head bolts could be just that...but it certainly does not do the head gasket any good. It could well indicate some warpage. I would expect some coolant loss somewhere with a bad head gasket; could be being burned in the cylinders. Any brown foamy stuff in the oil, on the dipstick or under the breathers? None of your symptoms so far indicate a blown head gasket.

Burned exhaust valves won't put combustion gases into the crankcase or under the valve cover; the leakage with those is between the exhaust system and the individual cylinders. The engine will run like the associated cylinders are dead or nearly so with burned valves.