It's been a while since I looked but I believe the gear sets were less than $20. I have one needing gears too. It hasn't been a priority to fix it yet. IIRC gear sets are less than $20 on Ebay. One of these days I might give it a go just for the experience. Any older machine with plastic gears is going to suffer the same fate sooner or later. The plastic is at the end of it's useful life. I figure it would be good to know how to replace them.
Rodney