Door closes fine. Opens half way & stops. Pressing button repeatedly to make it inch down, then inch back up again - eventually gets it open. Then I noticed that the door has some latitude to "slide" from side to side (about an inch each way) and when I physically "pull" the door sideways to center it, it opens without a problem. But it consistently & consistently "drifts" to the one side - and then I have the problem again. Any ideas ?? Is there some adjustment that keeps the door "centered" ??

Sears wormdrive opener (two years old), new track wheels as of last year.