Newby with milkshake in the oil pan 3.0

[Banjo5]

Hey guys. I bought a really nice Steplift with a newer 3.0. The guy I bought it from had it in the water like twice last year. Explained how he winterized it, and seems right to me. I brought it home, put the muffs on it and let it idle for 15 minutes or so to change the oil. When I drained the oil it was chocolate milk colored. Obviously, I was broken hearted. I did a little surfing and started trouble shooting by pressure testing the block. I disconnected the manifold and put 20# of air on the Tstat housing. It held pretty solid, so I think that means the block is ok. That really just leaves a couple options right? Maybe the manifold? I’m not sure if there’s anyway to test the manifold without pulling it, right? Are there any other leak sources I’m not thinking of? Is it possible that it’s just condensation in the oil size he didn’t run it much?