well, this is what the fiche for the 86-91 buses shows (and my old sensor
here in hand):
025 906 265 B   and it is a THREE-wire probe. it also has a Bosch part number
on it: 0 258 003 031     and another bosch number: (bosch symbol) 746 22 1
which, i think is some sort of batch and date of manufacture.

now ... the only problem is, it appears that i didn't hang onto any 83-85
fiche. :(  so i can't be certain that the 1.9l digijet engine has the same
probe. but the bentley book wiring diagrams appear to show it has the same
electrical connections. i'll call atlanta tomorrow and see what he knows and
what the price is.

i had asked once before at my FLAPS, and they said that they could order the
bosch part (3-wire) for about $50. the 1-wire version was about $30.

BUT!!! just because the light came on does NOT mean you have to replace it
right away. that light is tied to the odometer (electrically) and can be
reset (turned off) by crawling up under the bus front (by the spare tire)
and finding a small box inline on the speedometer cable. there is a shielded
button on that box. using a pencil/whatever, push on the button until it
clicks. then push on it again until you're sure it's been reset (but don't
break it). it took me three times to reset it.  the light is just a 'warning'
that you (the driver) need to be thinking about having the car serviced. as
far as the oxygen sensor goes, it's probably been replaced at least once
already, and if it ain't broke, don't fix it. :)

joel