Check between 2-4 clyinders and 5-7 near rear of head.The comp teat should have shown leakage between them in sense of similar comp both lower then rest Pull heads and have them checked do a valve job if needed. Low buck ? Pull heads then use a good straight edge check see if flat take and leak test the valves check block for damage. Put back together and flush out oil system with oil changes. I would change oil in one of my other cars dump that oil in run for hour then change it again with fresh oil.

PS. You have a serious leak so you might as well take it apart and check oil often after the fix