They all suffer of the same sickness, my 93-940 too, I bought one in eBay for $18 but then I found a better one in the junk yard for $5....it must be a bad quality rubber not adapted to extreme heat.

It's not difficult to extract and put it back in if you find one in the junk yard, don't worry about the overdrive switch you see in the back of the shifter, take that switch out before pulling up with both hands (and both legs)and cut off the two cables, put the switch back in later and don't even re-solder the contacts, just put some electrical tape and hide them...the overdrive will work automatically.

That switch is only used to "disable" the overdrive in cases you are pulling a trailer and you want the transmision to go from 4th to 3rd but that's not my case.

You can also go to the dealer and order one for $160 probably.

It's probably easier and cheaper to extract the entire shifter assembly from a junkyard car: you'll get replacement electricals with it too. The shift knob/shaft merely press fits into the shifter: see FAQ for removal instructions.