Correct me if I am wrong on this. There is a side on the radiator that houses a separate tank which contains automatic transmission fluid [ATF] that is cooled by, cooled engine coolant, I don't believe it is a conventional fluid cooler such as a transmission coolant specific cooler, but it partially works.
smoosh: How did you clean out the old radiator? I don't think you can run water through it but I could be wrong on that.. Did you just run compressed air through it to clean any gunk?
Some advice for purchasing a used radiator or any fluid cooler for that matter, is to check to make sure not too many fins a bent [a few will be normal], make sure there is zero rust through [if you can sand it off, make sure you do so and repaint it, also repaint any bare metal to prevent rust], make sure there are no bent tubes [if equiped] and that all the fittings have good threads and don't appear damaged, also make sure the main frame is not bent.
'89 SSE - GX3 -190k, 155k on body - Back for another ride.