Most of these refrigerators don't get much attention until there is a problem, so I would start by giving the unit and it's cabinet a good cleaning. Make sure there are no mud dauber nests on the coils. Also, spiders really like the smell of propane
odorant so they will make their nests in the burner. A fine, soft brush will get the cobwebs out, as will compressed air. Be careful with the air, as it will blow the jet right out.
Here is a link that will show you how to clean the burner.
That orifice is very small and just the tiniest bit of crud will reduce it's size significantly. Heed the warning: Do not poke anything through the jet to clean it. It's soft metal and you will ruin it.
The older absorption reefers are particularly sensitive to being off balance, as measured on the reefer itself. Side to side level is most important.
Good luck. Don't condemn it until you have given it a real chance