[Roger, here's a repost of my experiences replacing the thermal paste]

This is a "must-do" mod for anyone with a fridge:
-mike

I had an 85 with a Dometic that would barely get cold.  Turns out
they have a common problem:  The radiator fin assembly inside is
press fit onto a tube, with a layer of thermal paste between the two.
The paste dries up and stops working (and I suspect there have also
been improvements in thermal conductive paste technology in the past
20 years).

Procedure is as follows (for an 85, YMMV):

1. But two 1/4 ounce tubes of thermal conductive paste (aka "heat
sink paste" or "heat sink compound") from RadioShack.
2. Pull off the radiator fins.  It is press fit, can be tight, but
should pull off with a little muscle.
3. You should see some old, dried up looking paste on the fins and
the cold tube.  Clean this off.  I used hot water, my fingernails and
a washcloth.
4. Liberally apply the thermal paste.  I used two full 1/4 ounce
tubes and that seemed about the right amount.  Try to make sure the
paste is spread evenly without bubbles.
5. Press the fins back on, taking care to put the thermocouple back
in the groove in the fins.

Total time : about 20 minutes
Total cost : about $6

After this mod, the fins now get nice & frosty, and it has no trouble
keeping a reasonable temperature.

I also added a 12v matchbook-size fan to circulate air inside the
fridge, but rarely use it.   The biggest improvement came with
replacing the heat sink paste.

-mike