I was just working on my fridge (Dometic RM 36A) this weekend, from a 1972 CO Alaskan 8ft. The electric works, but the gas was too slow to cool. However, even the gas setting would freeze 1/2 cup of water if left on overnight in the freezer compartment. It also has a broken control knob for gas in the front of the interior, at the bottom.
Photo below: Control panel with busted shaft and knob for gas control.
I went to a junkyard yesterday, where they keep old RVs in the back. There was a Dodge CO there with an RM 45A Fridge that had the exact same controls, only a bit taller (same width). I pulled all the propane control valves, pilot and burner nozzles, and even the control shafts which run all the way from the front to the back. Cost $5 and 2 hours of my time.
I'm going to replace my control shaft and the burner nozzle assembly. I can already see that my original pilot and burner nozzles were not properly aligned, base upon what I have read. That may fix it (it may even have a colder gas setting that what I was stuck with, given the broken control knob shaft).
Another thing that may be affecting you: These old systems have a very thin, hollow copper tube that is used as a temperature sensor to the control valves. These tubes are no more than 1/16" in diameter (no kidding, see photo) and are very fragile. If cracked, they will not properly transfer temperature info to the valves from the interior of the fridge. There are two for a 2-way fridge: One for the electric controller and one for the propane controller. I broke one of the tubes as I removed them out of the junked Dodge RV.
Photo below--red arrows indicate the long copper tubes. Left box is electric thermostat, rightmost box (partial) is the gas thermostat (green arrow).
You can also just replace the entire thermostat, which comes with a new wire. About $60 online, search for "Ranko V35 Gas Thermostat" (if your fridge is same as mine). Hey, I already sunk $5 into this junked one, so I'll try that first, just for fun, if the control knob/shaft replacement doesn't work on its own.
Hope that helps. If one solves your problem, let us all know.