Water in oil five days after heads replaced

Initial problem was water disappearing from the radiator at a rate of 1/2 gallon a day. Then the engine overheated and blew the head gaskets and cracked the heads. We had a UTI student do the head gaskets, providing him with heads we purchased from a salvage yard that we took to a machine shop and had rebuilt and resurfaced. He didn't do a very good job and there was water in the oil the day after we picked it up. My husband re-did the intake manifold gaskets - twice - which did not resolve the issue. He finally removed the heads which we took back to the machine shop who magna fluxed and inspected and gave them back to us with the "all clear". My husband reinstalled the heads on new gaskets, reinstalled the intake manifold again on new gaskets and here's the fun part - I drove it for five days with clear oil, then yesterday suddenly the radiator was low a 1/2 gallon and today it was low a 1/2 gallon. I drove it approx. 25 miles today, came home checked the oil and all of a sudden there's about a gallon of water in the oil. My husband is a very good mechanic but we are stumped. We feel the block is not damaged so don't have any idea what else it could be except the intake manifold itself. Any input would be greatly appreciated.