liftmaster garage door opener (Boulton DE24)

we have a liftmaster 4210 EGB garage door opener with 2 remotes and a door switch, this was working perfectly till the plastic drive gear shredded. I had ordered a new unit when I found out that replacement gears were available, so I ordered and fitted the new gear. I have no reason to think that it does not work. I have looked on line and there are plenty of instructions on how to install, this operated a 10 foot wide up and over door