Our GB is 29 years old and has three boxes attached to the original compressor. About two years ago, maybe three, I noticed that it was remaining on for longer periods of time. I had a marine service tech come out to check things out. He had to add coolant to the system and checked for leaks (there were not any).
It's been running strong ever since. Our system runs for about 20 minutes then shuts down for an hour or more depending on the ambient temperature.
The tech showed me a little window on the compressor. It's a window to see the coolant circulate around the system. It's a good thing to not see bubbles rushing by the window. If there are bubbles present, then the system may need additional coolant.
Something to check out. BTW, I leave the system on 24/7, even when I'm gone.
1986 GB-42 Classic