It's worth noting that not everyne has had great success with Gerlinger gears:
http://www.bloomingstars.com/vega/ar...tmare/english/
They actually have a gear form that makes ACCURATE set up essential or the results can be poor. They seem not to have been taken into widespread use. There was an initial flurry of interest a year or so ago, but never eventuated to much.
An alternative is Jim Eggars at Aeroquest Machining:
http://www.aeroquest-machining.com/
who does a new worm for US$95 that several people have reported good results with. I am currently awaiting a reply from him for a total price including postage.
Gary