Believe it or not, C2 Corvette diff housings have a fill plug but no drain plug. It's almost impossible to get all the oil and sludge out of the diff without a drain plug. The rebuild of the rear end 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.