Repairing Sears 1/2 Horsepower Garage Door Opener

The motor runs fine on the opener when I push the button but the chain is not moving. When I unplugged the opener and checked on why, the inside of the opener was filled with white dust. My assumption is all of the dust is from one of the white plastic gears and the gear is worn down. My assumption now is the gears are not close enough together. There are adjustment screws on the side and the back of the garage door opener but I don't believe they would impact this adjustment. It did appear there was one plastic screw which controls how close these gears are to each other. Please advise if I should adjust this screw or the adjustment screws on the outside or if there would be another solution.
Thanks.