I think importers do compression test's on the motor when its cold.

Leak-down test time!

I think you can rent it from an auto parts store. It goes on your rad cap, then you pressurize the coolant system( do it on a warmed up motor).
My daughters mother had milky oil in her 96 maxima and I was pissed. Did a little research and found out the FWD vg30 has a internal water pump and when the seals go bad the oil and water mixes. This is not the case on an sr.