Had similar problem except previous owner damaged the threads and used the generic rubber plug which you press in with a special tool. Any ways what I did was pre cut a piece of 1/4" plate and tapped a 1/4" national pipe thread hole for my future drain hole. I then welded this piece over the old stripped hole and then went back through with the tap to clean up the threads. If wanted you could make the hole bigger and use 3/8 pipe thread. I find 1/4 is on the small side and you end up drinking too many beer watching the oil drain out. Other than the welding part supplies including tap is under 10 bucks. You could also try tapping the old hole to a pipe thread without doing the welding.