The question you have to ask yo self, and I don't think you have answered, is "what is causing all that oil contamination?"
All you seem to have done so far is find huge amounts of oil everywhere and clean it off. I suspect that reassembling it all without finding the cause, will result in a repeat.
Have you tried getting all the pistons at the same height (halfway up the bores) and pouring 50ml or so of oil in each bore, to see how long it takes for the oil to seep past the rings. If one pot goes down quickly, you might have broken or carboned-up rings.