An AC unit on its last legs will run longer and the compressor will run hotter until it seizes and fails. Difficult to monitor your current AC but on the flip side the number of hours of operation may be very small. A trailer used 3 weeks out of the year gets a lot less use than a house AC that is run for 4-5 months each year.
I have had sheepdogs for many years and I don't take them out into the desert in the summertime. They have very inefficient means for cooling down their body temp and they are not having fun either so I leave them at home with a house sitter. I consider it irresponsible to leave dogs inside unattended in 100 degree temperatures and would not think of doing it with mine.
A good reason for going with a new one is to right size the unit to the size of your RV. Most of the factory installed units are larger than is needed so they have shorter cycle times and do not operate nearly as efficiently as a smaller AC unit that has time to operate.
