A couple days ago my 10+ year-old 18.5 Magic Chef refrigerator lost its coldness and everything thawed. I re-plugged it in and it starting running but it only gets mildly cool and doesn't freeze. I have the coldness setting at the max. I gave it 24 hours to get back to its coldness but it hasn't come back.

The compressor seems to run most the time as I feel its vibration and heat and hear its hum. If I unplug the frig, turn off the temperature control, re-plug it back in, and after a few minutes turn up the temperature control to max, it kicks right in most the time. If I don't turn down the temp before plugging it back in, the overload clicks a couple times a few minutes apart before starting and sometimes doesn't start at all. Maybe the capacitor need to build up. Either way, the refrigerator still doesn't get cold enough and the compressor seems to be running.

I cleaned out the the back area of the refrigerator of dust. There is nothing leaking. no gurgles, seems a sealed system.
The condenser fan and evaporator fan are both running fine.
Tested the run capacitor for continuity and multi-meter reading seems fine.
Pulled the start relay and the overload continuity was good, the ohms reading good, and nothing rattled too much when I shook the relay. Although there was a small burn mark on the orange wire connection to the relay (but orange wire continuity was fine)
Tested the 3 prongs on the compressor for continuity and all are fine.
The temperature control, thermostat, and defrost timer look good as far as I can see.

Removed back panel of freezer to check the evaporator coils and defrost thermostat. Coils seemed fine and thermostat tested open. However, there was a big glob of frost on what I think is a drier tube on the incoming freon line and some of the perma-gum covering the tube had dripped on the coils. I knocked the frost off and cleaned it up. Not sure I need to replace the perma-gum around the drier tube as when I checked it a day later it had frosted up again?

I've done all I know. It could be the compressor or low or old freon? The manufacture doesn't make the compressor part anymore and there are no substitute available.

I am about to order a relay but not sure that would help, any help or suggestions?

Thanks