What would be the problem if you found oil in the back spark plug chamber on a 2000 Kia Sportage?

Answer

Hve you noticed any other leaks like anti freeze spilling into the passanger side foot rest. also if you bought it used if the rad mixture is chalky, someone mixed a sealant compound in to temporarily fix the leaking head gasket? if it is it could very well be a faulty head gasket, once they break oil can get into alot of places. get that checked before you get an 850$ repair job like i did. Goto mechanic asap.

Could be the valve cover gasket leaking there.

the problem is the valve cover gasket on the inside part has let go allowing oilo to leak into the spark plug tubes. Clean oput oil and replace gasket for valve cover.