transfer case/vss gear

i have a 95 explorer 4wd that just recently started to shift erratically, so suspecting a speed sensor i pulled it out and discovered that the gear had been chewed and was missing several teeth. i obtained a new gear and vss installed them and all was fine for 2 weeks when the same thing started happening again. i pulled the vss out and found that the gear was toast again. i did find that there was slight play in the output shaft of the transfer case and am now suspecting that it may be dropping the worm gear down so that it just barely is making contact with the vss gear. any ideas are greatly appreciated sam