What I did was sand the inside of the fitting until it would slide over the diff cup. It works great. It will seem as if you are taking off a lot of material, but don't worry. Dremel or sand it a little then try it until you can foce it onto the diff cup. If you don't have a dremel, wrap a piece of sand paper around a long philips bit and put that into your drill and use that to sand the fittings. It works.