I'm new to Mk2s - but there are few threads about adjusting auto selector linkage so I hope this is helpful
Mine has a later BW gearbox from a S1 XJ6.
It was very hard to get into Park, and felt like it may slip into reverse. There seemed to be too much strain on the cable.
Up underneath the dashboard are a couple of ball-jointed linkages - they are a pain to get to.
They have unusual spring clip ends - they unscrew, take th lock off the ball joint.
I wound mine out a bit to take the tension out - I went too far the first time (no Park, just reverse).
Lesson learned (with skun knuckles), now perfect.