I just took the original RM 100 out of 1976 31' sovereign. It still works on both propane and electric. It in overall good condition with the wire racks and plastic bins. No shipping pick up only. I am in the Houston TX area. If you want the RM 100 PM me for details.
I had it hauled off earlier this week. If yours will not work on electric have you tried it on propane. The electric heating element may be bad and they can be replaced. But first see if it works on propane. Here is a very good web site on RV refrigerators and they carry the parts for most of these old frigs.