I let my 2003 mustang 3.8 sit for 3 weeks and now coolant is mixing with the oil but no oil in coolant. We just had the engine apart and did all new gaskets including head gaskets. I changed the oil after break in and then once again after 300 miles and there was no water in it. I also had to break the water pump pulley loose because it wasn’t spinning at first. Just wondering if I need headgaskets again or if the water pump could be the problem. I also know it could be the intake manifold...

2003 mustang 3.8 coolant in oil