Believe it or not, C2 Corvette diff housings have a filler plug but no drain plug. The only way to drain the diff (while it's in the car) is to pump the oil out through the filler. It's impossible to get all the oil and sludge out of the diff using this method.
The rebuild of the rear end in late 2023 was a good opportunity to remedy this. With the diff out of the car and disassembled, SR Performance drilled and tapped a hole in the snout of the diff housing and installed a drain plug. A flush-fitting hex-keyed plug was used to give a factory appearance.
