Gene’s recommendation is a good place to start. His experience will save you time.
One other simple step is to check the fluid level in the transmission. If the seal at the front of the drive shaft fails the transmission fluid will transfer to the rear axle over time. So your transmission will be low on fluid which causes shifting problems. And your rear axle is over full which could cause leakage at the axle seals.
The next step would be to get a helper to sit in the car and move the shifter while you watch the various connections and pivot points on the total linkage system. That will help you determine if the looseness is at the transmission arms, in the box on the column, or at the shifter itself.
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