Yolo,
If it is one of the swing motor refrigerators, DC and AC only (no Gas operation, if you look at the back there is a big black can), then keep it going. If it works on DC then all the important parts are in good shape.
A manual is available at
GMC Documentation. This doesn't include a complete schematic, but I believe I have one that I could scan and send to you - if you need it. You may not. You may not. If you pull the electronics package out of the back, you will find it contains a relay that selects AC if it is available. The old version of that relay could be opened up. If you do, you will probably find some screwed up contacts that can be cleaned.
Just so you know, these units seen to only last about 40 years of serious use before they quit.
Matt