It pays to investigate.

A strange red fluid was leaking just under the back of the sliding door of
my van just under the rear seat area next to the side panels. Of course I
crawled under the van to check. Then under the seat.

It turns out I had a bottle of Marvel Mystery Oil upside down under the seat
in that area. That was the culprit. MMO bottle almost empty with slightly
loose cap.

For once it was a simple solution.
William