I'd keep the newer one if it passes all self tests and performance verification.
If there were any improvements made between the two serial numbers, it'll have them, and the VFD potentially won't have faded so much (depending on individual run-time, but replacement VFD's are available on ebay etc).
It's not too hard to replace the BNC's as they are still available. I replaced all the BNC's and the serial/GPIP ports on my 53132A just 2 days ago. They were damaged and rusted, now they are shiny and new.
