My 100-300 mk1 is heading back to
MPB for replacement on Monday. The manual focus ring on it is unusable, not just a 'bit stiff' but completely stiff, when you do manage to rotate it you get the lens jerking all over the place, not good for macro - which is the only reason I need MF on it.
@mpb.com wouldn't allow me to exchange for credit or refund, they say under warranty they can only offer a replacement, which is BS - if they'd allowed me to send it back for store credit I would have waited for them to get another MKII in stock. Oh well, the replacement better be in full working order, or we'll be to-and-fro for a while until I'm satisfied.