How important is it for hubs to be sealed and how weak are 28H hubs?

winston A lot of manufacturers (strangely) think track hubs will be used on the track! and as such pack very little grease in their hubs...for minimum resisistance....always a good idea to open up and rebuild new track hubs with as much grease as you can get in ....if you intend to use them on the road /in the wet....

Good tip, cheers for that.

I can't find those seals anywhere ! :( got a serial number on them ?

They are for a rear Dura Ace high flange.