I use FrostKing felt strips with great success.
http://www.frostking.com/felt-weatherstrip/
Open the door and staple into the wood frame.
Cheap and efficient.
I too have that opener. Same thing happened to me. Luckily, a friend with the same setup had the wheel strip out 3 months ago - so I learned on that job. I believe the Craftsman unit is a rebadged Chamberlain. I ordered just the wheel from Amazon - about $18.50 including shipping. Look for the...