Before you seal it for life by potting it, there’s a chance the issue is not so much the conductance of an oil soaked PCB but possibly thermal/vibration micofractures at the soldering points (bad Chinese soak solder process).
LG TV’s are famous for their crappy motherboards dropping HDMI inputs. We’ve set the toaster oven to 450 F and baked the board to bring it back to life. Might need to do the same with the locker HET sensor but potting it will all but guarantee taking that option off the table.
I like the no drain plug. You can use the fluid evacuator to get it out. That way you don't break the cover seal. That's how I would change it if I didn't have the drain plug.
Has anyone done this? Have a friend in Colorado who has a business and has about 15 vehicles (trucks) does heavy maintenance all over with a lot of driving. He told me when discussing this thread that for almost 40 years he changed his differential fluid by draining about 30 percent of the fluid and adding kerosene. Then drive for a while until good and warm. Then drain immediately. Cleans everything out. These are heavy duty gas and diesel trucks 1/2 to 5 tons. Job site vehicles. He does this every time he changes oil. These differentials are upwards of 8000 dollars. He has never had any problems of any kind and yes there are some (most) 4wh dr. With electrical cylinoids etc. He is still working and doing his own maintenance.I think you're misunderstanding what's happening when the sensors fail. It's not cold/cracked joints.
They're failing because the gear oil has metal flake in it which is shorting out 1 of the 3 capacitors on the board. The potting material is just keeping the gear oil from getting to the PCB.
Nothing more than that.