Today I went to the local yard with one of the UCAs that I knew was not seating correctly on my wagon. I tested it on the following: 1978 116, 1985 123, 1979 123, and 1985 (?) 126.

The point of contact between the spindle and UCA ball joint ALL sat indentically (of course the lengths and exact configuration of the arm itself differed, but I wanted to see how that threaded section from the UCA sat when inserted in different spindles) the ball joint bolt has a tapered design at the top and can apparently be insterted approximately 5-10mm before directly contacting the actual ball of the ball joint - see the images above with the rubber bushing compressed between the two parts.

I'm baffled