Here's more info. and symptoms.
I tried to engage "winter" mode to see if that would make any difference, but the arrow would not illuminate on the instrument cluster. Could hear a noise somewhere when pressing the "w" button but it does not appear to have engaged. For some reason, I think you can't engage winter mode above a certain ambient temperature. It was about 80 F or so at the time. I'll check the manual.

I did row the gearshift back and forth to no avail and the fluid looks great and is at the proper level. Still bright pink and doesn't smell burned at all.

This car is a 2001 1.9T North American delivery with what I've always assumed is a 5 speed (automatic). Shifter indicates P-R-N-D-4-3-L.

Maybe my Dex III drain / fills from 147K to 173K miles (26,000 miles) destroyed the transmission.
Or maybe the 12,000 miles of 3309 spec did?
Or maybe the transmission just has given up after 185,000 miles.

Took it for a ride this morning and here's what happened.

Car sat overnight. Ambient temperature 68 degrees F.
Cold start normally and the CEL comes on - P0600 according to my ScanGauge II.
P0600 comes up as a generic Serial Communication Link Malfunction.
Sitting in the driveway, the transmission acts absolutely normal. Smooth shift into Reverse, smooth shifts into Drive, 4, 3 and L. Creeps forward slowly when letting off the brake and in Drive. Just like usual.

Pull out of the driveway and go up the street. Left it in Drive and it shifts normally through all the gears. Included a few stop and starts and still the transmission is working like it should.

After about 2 miles I come to another stop and I can hear a distinct slight whine coming from under the hood. Shift to Neutral and the whine subsides. Shift back into Drive and the whine starts again and the car is in what I assume is limp mode (appears to be 3rd or 4th gear). I didn't want to try Reverse as that previously resulted in that destructive sounding BANG yesterday. Tried shifting to Low in hopes of being able to start off in 1st gear, but that made no difference. Regardless of where I put the shift lever (in forward gears) the transmission stays in limp mode.

I'm now thinking the problem has something to do with the transmission temperature and that whining sound. I thought the UP arrow is supposed to flash if there is a transmission malfunction, but that hasn't happened yet.