Over in the Delaware Water Gap area a few years ago, I look at a private seller's car and found the same thing. Also, the Purolator oil filter. some awful-looking home-made alternator wiring fix.

The seller could not give me a good explanation for the milky oil under the filler cap.

so, I excused myself and headed for my car. Before I left, however, I asked to see his minivan, which he also was selling.

Guess what?

that had milky oil too!

I never heard of "it's only condensation".

Without appropriate and satisfactory compression and leak down tests, I'd pass.