+1 and +2 above.  I have the same RM 8501 as you in a 2011 177.  Worked real good until a year ago when it developed an ammonia leak.  Had to replace.  As far as parts, if you are certain about a particular part you need, I may still have it available for you. 

A few years before the failure I was having similar issues.  Had to replace both the regulator (from the tank) and the line from the regulator to the fridge.  Both were mucked up with the oily substance from years of usage of propane.  Now I know to shut propane off when not using for a month or more.  Also it helps greatly if you move your bi-metal switch close to within 2" of the cooling stack.  They come from the factory located about 5 fins to the left the the cooling stack - move it all the way to the right within 2".  This will cause your two muffin fans to kick on sooner and run longer resulting in much colder interior temps.  This switch can easily be located by finding two red wires that end at the switch.

As for getting cold, cleaning the burner/chimney tube is important as is cleaning the orifice (no pins, needles, etc.) with rubbing alcohol. You may also have an oily build-up in your gas lines. Remove the gas line from the back of the refrigerator and from the regulator. With the regulator end of the tube in a bucket, use a compressor to blow air from the refrigerator end. You will likely be surprised at how much oily liquid is in there. Reassemble and test for leaks. Then purge the lines and see if it makes a difference. It did for me.

It's a Dometic 8501.

have you cleaned and blown out the back? The burner tube/chimney? Checked for anything blocking airflow up and through the back?