Im just going to use Ankor wax and leave the outside. Inside and underneath will all be painted and sealed.
The Watts link is better than a panhard rod but dont get used much in production cars because of the extra parts required. Most race cars with a live axle use a watts link because the roll centre can be easily moved.
I used it because the rails are narrow and a panhard rod would be very short meaning the diff would move sideways quite a bit through its travel range.