Okay, just to make sure I don't simply need an adjustment instead of a replacement, are you saying that the area in the picture below with the red arrow cannot be tightened up, but is just worn out and won't get any tighter? I noticed in the shop manual that it said there will be 1mm of movement (of part 11 towards the steering box) as a result of tightening the lock nut (but it does not imply that there should be any play after it is tightened).
Excerpt:
During tightening, the stop surface at the steering stop ring shifts by approximately 1mm, i.e. adjusting distance a must be checked and readjusted, if required, after the lock nut has been tightened.
And another picture from the shop manual that is referenced by the excerpt above:
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99 996 cab: 2004 - present,GT3 & Strosek mixed body
86 951: 2008 - present,951MaxChips,LSD,LBE,924t hood & rear spoiler, Koni/Eibach/Ground Control, 3Bar FPR, lowered,brake cooling, Lindsey spherical bushings
99 986: 2002-2006, PSE (my favorite of the three, but with kids, it had to go)
1986 951 pic