Fortunately for me I had the original invoice from B&H, and Vivitar has a 1-year warranty. The experience of calling these guys up was surprisingly relaxed – there’s no RMA number you get, no tracking info, for that matter, there’s really no authorization process to speak of. I could have skipped the call and just sent them the flash along with a little note saying “its broken – the zoom clicks and it stops at 28mm” and that’d have been fine.
Yesterday I got my box back from Vivitar with a brand new DF-383 inside, for Canon, no less. It’d have been charming if they sent a Nikon flash. While their support seems a bit minimalist, I can’t fault those guys for a decidedly no-hassle experience. The real test will be if the new unit lasts more than 6 months.