If you ever want to check the voltage to a brushed motor all you have to do is use a multimeter set to DCV on the solder tabs/joints where the motor connects to the esc wires. That being said its not that important what the actual voltage is as long as its low rpms.
Even if you didnt chip or in...
A long time ago someone told me over on RCTech (IIRC) to run the motor at 3V for 20-30 minutes. I'm not sure what voltage you ran yours at or how long but that was a guideline I was given. For bearing lube I like Acer SIN lube.
For $60 you can get an Adjustable DC Power Supply from Amazon. Thats the one I have. Buy some allagator clips and run the motor on 3v for about 20-30 minutes while submerged.
If you have an old computer power supply laying around it can cheaply and easily be converted to be a benchtop power...
I didnt mean for softening the brushes, I just meant if comparing submerging it in anti-freeze vs water. As you say the PG is a better lube than water and the inhibitors will help protect the copper and other metal parts from corrosion. Not saying you can't prevent corrosion if you did use water...
I could see where anti-freeze would be better than water. Modern anti-freeze has all kinds of corrosion inhibitors in it that coats the metal and protects it. I have no idea about comm drops.