1988 XJ6 reverse going going gone

I just bought an 88 XJ6, the reverse was pulling real slow the first couple days and now it is gone. When I put the car in reverse I do not hear the gear kick in and the car will not move. I assume this is a transmission problem, in drive the tranny seems fine, alittle slipage from 1 to 2. should I be concerned that the transmission will go completely soon?

Thanks