I think that's probably the best decision for you. An operating 5972 is OK, but to ship one and then set up, being that it's out of support, is a gamble. I'd say the chances of it working within a week for you would be 80 to 85%, not horrible odds though. If your neck will be on the line, then go for something like the 5973 if you can get guarantee of operation, maybe a vendor like Alpha Omega (AOT) or Linc Quantum/Quantum Analytics who deal in refurbished/guaranteed Agilent systems.

I don't think that cleaning the source on the 5971/5972 was that bad, the biggest issue might be obtaining certain parts. So I guess that I would keep old operating instruments operating, and just have a plan in place to move quickly when they cannot be repaired due to parts availability. It's like driving a collectible car - you just can't run down to the corner store for parts.