Thanks for the advice! I jacked the car up so that the wheel in question was about 3.5" off of the ground. I then stuck a four foot 2x4 underneath it (between the wheel and the floor) and pried upwards. The shocks / springs / car all moved, but there was zero movement in the ball joint. I also don't hear the other symptoms you describe (groaning / creaking / knuckling).

I had a 190E with bad tie rod ends, and the wheel would easily wiggle horizontally with the car jacked up. I assume I would be looking for a similar type of movement / free play in the vertical direction if the ball joint is bad, and I don't see this at all.

Unless there's something I've missed, I'm going to assume that the inspection facility is wrong on this one and see if I can get them to take it off of the report (they already listed some other things that don't need doing, just because 'these things usually go on old cars').

I ordered the parts to do the subframe mounts - I'll give it a try on the weekend and see how it goes. If I can't do it, I'll just take the parts somewhere and get a mechanic to do the work...

Matt