What bearings does he use Doug? I would be using timkin, not happy shopper ones.
And get them pressed in rather than impacting

If that doesn't work then its simply a case we have pushed them past the limit of the std bearings so bigger and stronger is the only way forward,
I would advise short term sourcing a set of hubs and arms and have new bearings fitted in them so they can be swapped at events quickly should another failure occur, I'm sure they are pretty easy to get hold of for cheaps.

Which one was it? The O/S/F collapsed at round 1