30 year old Norcold fridge

[dutchduo1990]

I have a 30 year old class b in very good condition but my fridge is giving me trouble now and I can’t spend $1200. On a new electric fridge. I have emailed Thetford but no replies.
My fridge is a 12 v - 120 v. I can’t get the temperature colder them -11 in the freezer and 7 degrees above 0 Celsius in the fridge.
Once the fridge shuts off the temperature will drop down to 0 in the freezer . Is there any adjustment anywhere to make the recycling shorter so it will only drop a few degrees.
What about a 120 volt fridge running on an inverter.