Actually, I've found there to be "early" and "late" OBCs, but don't quote me on that (haven't done enough research to justify it beyond an assertion). I have, however, seen similar looking OBCs (ie - '95 into '90) work on some functions, yet not others, specifically fuel economy/miles to empty. It may be a DME specific case, I don't know. The OEM manufacturer changed sometime during E34 production (to siemens or from siemens, I forget...)

As mentioned in the engine/trans swap/rebuild thread, stay away from that seller. Nothing but bad news. It's okay to pay other people to work on the car (although, it's my humble belief that the enthusiast turns his own wrench), but please don't make the mistake of buying parts from unreliable and dishonest sources.

best, whit