Here is my honest advice based on experience of buying no less than 7 Z4000 transformers (4 for our local club).
#1 While under ideal conditions (price mainly) side by side, you would choose a newer version (serial number higher than 0398). However, given the high prices, paying significantly more for the minor changes does not make sense to me. The 2 differences that matter are the adjustable friction plunger system on the handles and the voltage leak fix are improved over the first versions. Neither of these features is worth hundreds of dollars in cost difference. Voltage leak can be worked around with something as simple as a light bulb as load.
#2 If it has to ship, you better have the original Z4000 box and foam inserts. Bubble wrap, foam peanuts, crumpled paper are NOT enough to protect this heavy transformer in transit. You will likely break the control handles off or crack the feet and lower base housing during shipping if the original high density shaped foam inserts and box are not used. these are heavy and bulky and again, likely will break the housing, break the handles and maybe even break the heavy transformers free inside to cause serious damage. I had to write more than one off as a total loss and return to the seller as a pile of damaged parts because of improper packing materials and shipping.
Again, in my mind, the biggest factor and not talked about enough- you should choose one with the original box over one without the original box. That's true even if buying locally because if you need to fix it and ship it- this could come up again.
