Upload & Sell: Off
In all of the testing I did, I found that my ZM 35mm C-Biogon had lost some dampening in the focus helicoid through most of the range, but got tight at infinity and MFD. It was still under warranty, and I sent it into Zeiss. I figured they'd just relube it, but instead they're just sending me a new one. Awesome service, took 1 day for them to decide. But it does make me wonder what they found under the hood.
I doubt there is anything seriously wrong with the lens. Rather, it's a matter of it being easier, cheaper and faster to replace the lens on the spot from inventory already in the USA, rather than ship it to Germany and get it serviced on their own coin. And realistically, for a roughly $800 lens, their cost is probably ridiculously low, to the point where service labour could easily be higher.
FWIW, a friend here is a Zeiss dealer and he says this is fairly typical - that they'll replace rather than repair.
It's quite possible they stockpile the returned lenses and at some point have them overhauled in order to resell as refurbs or use as demo stock.