It's been a while since I flew the B737-400 but I seem to recall they came without a cargo fire detection system as fitted to the -NGs. Instead the holds were designed to suppress a fire for 30(?) mins. (I think they were called class D holds).
The lining of the holds had to be intact as this is what provided the suppressant, any tears or damage had to be fixed using a fire retardent tape. If the hold could not be repaired I seem to recall we could continue to use the hold provided no flammable items were carried in that hold. Obviously all the limitations and specifics were incorporated in the wording of the MEL, which would have been specific to the company I was working for at the time.