I'm down to my last few bits of kit as I exit the volt-nut world...
Fluke 731A DC Reference Standard -- batteries replaced in mid 2020. I made no attempt to adjust the absolute voltage (as per advice here and elsewhere.)
This is fully working and very stable, it's been on consistently since mid 2020 and at least for the last year or so has been measured by one of two 3458A's (not recorded, just sits in front of me while I do my day job!). Just recently I had one of the 3458A's calibrated and remeasured (helpfully getting the same result), so I measure the 10V output at 10.000158 to within a couple of uV consistently after an ACAL.
I haven't monitored the 1V or 1.018V outputs, but they also seem stable at 1.000012V and 1.018019V (I've sold the 3458A's now, so this is measured with a DMM7510.)
I was hoping for £1500, but make me a sensible offer.
This one is probably shippable, but obviously not ideal given the need to keep it powered up. So prefer a pickup from Poole (Dorset), but happy to discuss options.