The first thing I would check is the drive block. In order to do it you have to remove the cabinet and the agitator. Here is the
complete instructions how to remove the cabinet and
how to remove the agitator.
Remove the tub ring unsnapping the tub ring tabs from the tub one at a time.
Next step is to remove the spanner nut. You can do it using a hummer and
a screwdriver or you can buy a special
spanner wrench
Carefully remove the basket by lifting straight up. Using a hummer, carefully tap up from the bottom of the drive block to remove.
Inspect notches on the drive block and tabs on the spin tube. If notches on the drive block are worn out, replace the
drive block
If the problem is worn out tabs on the spin tube there is more serious job because the spin tube is a part of the basket drive/brakes assembly and to replace it you have to remove the gear case (aka transmission). Let me know if you are going to do it and I'll help you.
Good luck.
Gene.