It was the motor on the side of the case in the passenger footwell. i noticed that motor wasn't moving before, but find it difficult to do diag when somebody is looking over my shoulder. Three screws and it's out. A bit tougher to get back in as the doors linkage arm drops down due to gravity...I'll snap a picture of another van later. Didn't realize the heater core is there lying basically flat. The motor moves a blend door.
1.Loosened dipstick tube bracket and pulled out.
2.Removed starter <wanted plenty-o-room> and drained oil into a bucket. Owner uses Amsoil and it was just changed.
3.Bent a V shape on a piece of heavy wire and stuffed it in the "adapater".
4.Removed and pushed "adapter" inside pan and allowed to gently settle to bottom.
5.Cleaned pan inside and out.
6.Pulled "adapter" up to remove o-ring and found o-ring was broken, that's why it was leaking.
7.Fed new o-ring up wire and stuffed it thru hole and into groove in adapter.
8.Pulled adapter into position and installed nut with a bit of red loctite.
9.Changed dipstick o-ring and re-installed tube.
10.Re-installed starter and oil.
Took about the same amount of time it took me to type this...
Thanks for the help guys. The part numbers made this really easy.
Next have to figure out why this truck eats belts...customer says it's been on-going for about two years. Only thing left on the belt driven system that hasn't been replaced is the PS pully or pump! I removed the belt and checked for failing vaccum pump, idlers, pulleys, etc...tensioner didn't wobble when being moved.
Ran out of time as they needed the truck. Will bring it back later.
ktmlew's post in 2010 Chevy Van Heater was marked as the answer