Couple of tips for PM'ing the Aventa towbar, the one that has the "piviot ball". The washer set, available from various sources, contains all the needed nylon washers. It does not contain any washers for the pivot ball itself. Inside the pivot ball are a set of brass semi spheres and a spring washer that provides tension for the "pivot" function. Clean the components but do not lube them. The Blue Ox video
https://www.youtube.com/watch?v=WS2PPnlTqXo notes that when reassembling there should be about a .25" gap between the top and bottom ball halves and if not, either the spring washer is bad or a brass washer needs to be added as spacer between the spring washer and the semi sphere. Calling Blue Ox I learned that they will not supply the spring washer but want you to ship the unit back to them and they will replace it. I guess they want to check for severe wear etc. Mine showed no evidence of wear so I located the parts elsewhere.
The spring washer is available via Fastnels. Mfgr is Willie Washer. Part number is 2.000-1.015-.065 HHB (2" OD, 1.015" ID, .065 thick). While mine didn't appear worn, I got one a for future use. The brass washer is available on Amazon. Best way I found to determine correct thickness was to wrap various sizes of wire around shaft between washer and globe to get the desired 0.25" spacing and then measure the wire thickness. Mine needed a 0.060 washer. Reassembled and seems good for another few years.
Steve