I doubt a bottom dust seal is necessary. There isn't one on the taper rollers used for Healey steering head bearings and I did nearly 40,000 miles on my previous Healey without even greasing the steering head bearings. Handling was always excellent.
36 4G, 37 VH, 53 ex ISDT KHA (project), 54 KH(A), Healey 1000/4 (project)
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.