although there are tolerances on the shim clearances, some dealers still like to work to their own, slightly tighter ones, closer to the lower limits and will adjust to these if they think it necesary/beneficial
'strettas do seem to hold their clearances better.
as for rockers, the older 4V's will still flake the "new improved" items, if abused and i've seen a couple of 'stretta ones let go to, although they are very rare.
Look after them like the old 4V is my advice
