I’ve never used Blue Devil Stop Leak. I looked ar the instructions, which were brief and seem incomplete.
“Directions: BlueDevil Oil Stop Leak
1. Pour 1 bottle (8 oz.) into leaking component’s oil sump, or crank case.
Treats 4 to 6 quarts of motor oil.
2. Start engine or equipment and operate for 1 to 2 hours or until leak has
stopped (for extreme leaks up to 2 days drive time may be required).
Use this product for: pinion seals, gear cases, refillable shock absorbers, gear
boxes, axle seals, and gear differentials.”
In the case of a differential are you supposed to remove 8 oz. of differential oil before adding the stop leak? And then what? Do you just leave it in? Or do you drain and refill?
I would be cautious about doing anything that would increase the viscosity of the differential oil for any more than a brief period. The synchronizers in the transfer case depend upon the diff oil not being heavier than specified.