LEAK DOWN TEST HAS NOTHING TO DO WITH OIL RINGS , IT'S TESTING THE VALVES AND FIRST AND SECOND RINGS. if the air comes out the oil tube then the first and second rings are the problem. Are the pistons and rings the correct sise ie. standard / 10 over / 30over etc. . Make sure the pistons and ring are for the same size bore. The first ring is what seals the cylinder on the compression stroke. Thats all it's job is in life nothing else. The second is a double duty ring so to speak. It counter seals the the top rings " gap " , thats why you don't line them up. So make sure you put the rings on the pistons the correct way. They have a top and bottom as well as a final location to be in when in the cylinder. The second ring second job is a final oil scrape. the oil rings just do a fast heavy oil scrape to make sure the second and fist ring don't get coverd !
I don't think you have to rebuild completely just recheck the end gap of the rings and their sizes and correct position installed.



air out the exhaust is e-valve
air out intake= intake valve
out radiator (bubbles ) head/block or head gasket