Liftmaster Garage Door problem

I have a Liftmaster Professional garage door opener...I think it is Model 1255R. Well it stopped working the other day, my wife says nothing unusual had occured. Motor turns, but door does nothing.
So I opened the housing and found that the plastic gear that drives chain (I believe it is called Drive/Worm gear kit, part 41A2817) is gone. Well, not gone...but the teeth are gone.
So I found the various sites on the net to order one. But what I can't quite figure out is how do I get that piece out?
Anyone know?
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snipped-for-privacy@gmail.com wrote:

http://www.1stdooropeners.com/liftmaster/parts.htm
I've ordered stuff from these folks & they sent directions with the patrs. I suggest you give them a call & see if this kits comes with directions.
cheers Bob
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First remove the chain from the opener, but put make a mark somehow on the chain to put it back on the sprocket in the same place. Remove the fork piece that holds the small limit gear at the bottom of the shaft & remove the limit gear. Remove the three screws that holds the shaft plate to the top of the motor head. Pull the whole shaft assembly out thru the top. Put the shaft onto some blocks of wood & drive out the roll pin in the bottom of the worn out gear. Change the gear & re-assemble in the opposite order. You may have to make small adjustments to the limits to get the door to open or close fully.
Doordoc www.DoorsAndOpeners.com
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Follow the instructions in the parts kit. Suppliers on my Web page:
http://www.truetex.com/garage.htm
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