Probably the shift linkage bushings are worn.
Little nylon rings - they allow more slop in the action when they get worn.
Car has two, they cost $.85 each from fcpgroton. One at tranny end of lever/bar, the other is a shifter end.

Install from under the car. Only takes a few minutes if you have a real shop lift. Probably a real PITA if you're doing it in a driveway.

Yes, there is an adjustment to the backup light switch. And broken/worn engine or tranny mounts can also throw off the position + alignment of that assembly. But if you can easily move the shifter +/- a quarter inch, I'd guess that the linkage bushings are worn. With new bushings you probably can ignore the switch adjustment.
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Sven: '89 245 NA, 951 ECU, open-front airbox, E-fan, 205/65-15's, IPD sways, E-Codes, amber front corner reflectors, quad horns. Wifemobile '89 245 NA stock. 90 244 NA spare, runs.