The mystery of the missing oil?

"what if it only leaks going down the road"

And what if the tooth fairy is stealing it??
Cool jibe, bro, but I've seen \6 oil pressure senders (for one example) leak under pressure in such a manner that there's little or no evidence. You lose your oil on the road, but not on the driveway or garage floor.

There are a lot of things to like about the Slant-Six engine; there are a lot of things it does very well. Keeping the oil inside is not one of them.