I have greased a de dion tube, and then used oil filled seals. This seems to work well. The tube was pitted so oil would most likely just leak out, then end up in the rubber boot, hence I decided to use grease.
I think you can use the felt seals in place of the oil ones. However I cannot see any of them for sale from the usual suppliers. If I recall correctly they used to be listed, so I suggest that you just go with oil filled seals like I did. You may be able to find o rings which will work as well. I knew a Rover mechanic in Adelaide who did this.
James.