A170 oil in air filter box

[monstermaker]

I have had a problem with my 2005 A170 burning oil. This causes it to burn up spark plugs and eventually misfire. After many spark plug replacements which solved the prob for a while I found that there was oil in the air filter box. I don't mean a bit of oil but a couple of inches of engine oil. It looks like it's coming out of the air intake. Anyone got any ideas. I originally suspected head gasket but check proved not.