Meanwhile I put in a new stereo--the original was a cassette with 6 disk trunk-mounted CD. The CD player wouldn't play CD-R's, and the cassette auto reverse was based on volume rather than end of tape. This made using an adapter to play MP3's a problem, because at gaps it would reverse back and forth, and if you didn't start the MP3 player quickly enough it would spit the adapter out.
Turns out that diagnostics for the ABS system come through the radio plug, so the mechanic had to remove the new radio to read the code. And the factory radio shoved a splinter of plastic into my thumb as I was tossing it in the trunk, on my way to work, when I was running late.
The new radio is fantastic, and is working out just as I planned. I've got music on the USB drive. I can shuffle either a single folder or the entire drive. I have my music organized into folders based on what my wife and I both like, and what only I like, depending on who is riding. I've got podcasts on a CD Rewritable, and they stop and start without losing my place when I start and stop the car--this was the main reason for the new radio, and alone worth the switch.
One minor downside is that apparently the VW antenna is weak, and apparently needs an amplifier. I can pick up only one station. Not a significant problem--I can't think of the last time I listened to the radio except for a short trip out of laziness.