Group
The Mk1 hubs are very fragile and should be replaced at the end of every season. I have had two Mk1 hubs fail in nine years of racing and luckily both failures occurred in parts of Summit Point where I was able to coast the car to a halt with without hitting anything.
MkII hubs are less fragile but will fail eventually (and just as spectacularly as the Mk1 hubs).
MkIII hubs are very stout. But like any racecar part they should be replaced regularly.

I have no experience with the MkIV cars in racing trim. But I have taken apart the wifes street MkIV and the design seems to be better than the MkIII.

cheers
dave parker