McCormack Screw compressor oil heaters

I received a call from my old employer today.
Years ago I replaced a oil heater in a screw compressor near here. The unit has two heaters installed in 3 or 4 inch block welded into the oil sump.
According to the operator that heater is still operating fine.
However the replacements seem to be overheating and burning out fairly quickly. I have not looked at the machine, but I am told that the replacements have a side clearance of about 1/8 of a inch when installed. (Being retired I will not be seeing the machine)
I do not remember using any heat transfer compound when I installed the heater, nor do I remember if there was excessive clearance. We would have bought the heater from the OEM.
My usual procedure was to use something like a Nickel based Anti-Seize compound.
Removing the functioning heater is not a good plan as it may well break if they try to remove it for identification.
The OEM (McCormack) is no longer in business.
Can someone suggest a heat transfer compound that can be installed in a vertical application?
I actually worked for the OEM at one time, but I do not recall what we used.
I have asked for an Amp reading from the functioning one so we can determine the electrical sizing.

Really nice to hear from you "Old Timer"!
If I could I would help.
But Sadly the kit you need help with is something I have not come across on this side of the pond.
Out of interest are the Heaters wired in parallel or series?
Cheers Grizzly

Same to you Grizzly.
Do not have much to post about these days. Sure nice to do other things than get up and go to work. I do not know how I ever had time to have a job.
The heaters fortunately are in parallel.
Only one heater working is a problem as although they are inside the area is cold.

NH3LVR,
Not 100% sure but older type immersion heaters we used were filled with fridge oil & had a breather hole so to allow for expansion etc.
These pockets were on 30 deg angle & breather at top part of pocket.
Heater had a t/stay up the middle like Vilter.
Some other heaters, no pocket, but direct contact.
If it is sealed & filled with oil or heat transfer paste there is a possibility for hydraulicing pocket if no vent.