For those of you with 1989 thought at least 1993 models, I think this is the unit that Airstream used. Until recently you could not buy direct, but looks like now you can. Both my 1991 and 1993 had really deteriorated, with broken plastic screw bosses and broken off bulb holders on the 1991. I just got the 1993 working again today, but I am going to order a spare, as its days are numbered.
http://www.esierra.us/Qstore/Qstore.cgi ... 1025634615