40 degrees Fahrenheit is the absolute maximum temperature that potentially hazardous foods can be kept at. Anything above that and you are asking for trouble. Additionally, the longer time that the food is kept at that temperature, the more hazardous the food becomes. 35degrees F. or so is more ideal.
skipg: My Dometic RML8555, brand new has never done any better than yours and its sad that we consumers are saddled with these lousy appliances. As a side note: my two friends who bought new rvs that have the same fridge as I do, had the same problem also and Dometic's response is that that's the way they are. One friend spent $$$$ and switched to a 12volt compressor fridge and the other spent $$$ trying to repair something that couldn't be fixed. Myself, I've given up.