Not sure what you mean by oil leak....if you mean signs of oil in and around the oil filter/ turbo....Several places to check,if you are sure that the filter is tourqued correctly and you did smear the rubber casket with oil, and the matting surfaces were clean (no left over garbage from previous filter removal)...On turbo, check the oil feed and return lines, check return line at block as well, there is an "O" ring on the block side of the return line which may be shot; also the block side of the oil feed line (just to the left of the oil filter..about 11:00) may need to be tighten a bit.....On the other hand, if you mean that you notice blueish white (oil) smoke from the rear of your car, at highway speeds...and especially when you up-shift...the turbo oil seals are going (gone)..this I speak from current experience. Hope this helps you out....keep us posted...thanks..Al