You can't really tighten the shifter...I've replaced the bushings in the linkage, but you really have to replace the shifter assembly if you want a tight feel.

I replaced the shifter on our since-sold 1987 760T around 220K miles after a series of issues with the detent button/shaft. I could have fixed the shaft with a roll pin (the piece of soft nail kept shearing) but just gave up and replaced the entire assembly. New ones were available and probably still are from the dealer...I paid about $180 USD for it and it went in really easily. I also replaced the wire from the overdrive switch...it is NOT included in the shifter assembly! The old wire insulation was breaking down and although no shorts it was just a matter of time. Too much oil and junk under there.

So go ahead and fiddle around with bushings if you want, but the best way is to replace the shifter. How about buying the tight shifter you found at the junkyard? It's only about 20minutes to pull the shifter from the junker! The worst part is getting under the car to release the linkage.