I would be willing to bet a few coins that in the course of 2k miles, the process of opening the pan drain and fill tube to open air there is more contamination happening than what the trans wear put into the fluid. I mean unless you use your 80 to haul mobile homes for a living.
Much cheaper to do it yourself, but also much dirtier.
Better to do a complete fluid exchange
More better to drop and clean the pan first.
Easier to do multiple drain and fills.
Safer to add an inline transmission filter before you start drain and fills
as you do stir up the sediment (proven by serial Blackstone ATF reports)
Never reuse the drain plug crush washer (new washer every time) and never gorilla grip the wrench when tightening the plug.
I do appreciate all the thoughtful responses. At another time in my life, I would certainly have followed the advice and done it myself. Unfortunately I've got chronic back issues that preclude my taking this on myself at this point.
So short of another recommendation for a mechanic in Contra Costa, Solano or Napa County, I probably will have to go with these guys.