We have two B models with Brakesavers, and we drain the retarder as well as the pan. As @techmech said it probably isn't necessary, but you will get another gallon maybe out of the retarder. If you really want to get carried away you can drain the two little plugs to drain the tubes going to the pan.
A forum community dedicated to Diesel engine owners and enthusiasts. Come join the discussion about performance, builds, ecodiesel, towing capacity, modifications, classifieds, troubleshooting, maintenance, and more!