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, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.