I picked up the obd-2.com tricom scan tool and software and found a failure in the front O2 sensor. The guy at the area code 630 number is actually an auto parts guy, MidTex Auto in Chicago. He suggested that I replace both heated O2 sensors since they work in tandem, measuring the O2 difference between the front and back of the catalytic converter. He mentioned that they had found empirically that the generic Bosch sensors offer, comparable performance but that you have to re-use the wiring harness from the old unit.

The cost difference is roughly $100 to $150 extra per sensor, with the generics running about $50 as mentioned above. A shop could try charging you a couple of hours labor, so it's possible you could easily spend $500 on the repair.

I just picked up two of the Bosch 15715 generic O2 sensors (4-wire). The claim, both here on brickboard.com and and the shop I bought them from is that you can cut the 4 wires near the old sensor and splice the new sensor in (i.e., reuse the old wiring harness). Do a search for oxygen sensor 850 on this board for more details. I'm going to give it a shot this weekend.

BTW, I paid ~$49 ea. for the generic sensors at MidTex (630) 904-5745. By comparison, the OEM Bosch parts for my (manual trans '96 850GLT) were 13373 (~$135 at MidTex - up to $200 elsewhere) for the front and 15062 ($146-$220) for the rear.