Years ago, we had an LP fridge
that leaked out. The point of leakage was accessible, and a repairman was able to solder and recharge the ammonia. It worked for several years after that. I think, however, that successful repairs are uncommon.
My parents have a 12-year-old 5th wheel, and their fridge
was dead at the beginning of last season. They went up to Bill's RV Appliance (as mentioned by pjantis), and had a new cooling unit installed. It saved them several hundred dollars, and is so far (second season now) working just fine.