The pinion set (4114 640 7300) inside the gear head assembly (4121 640 0100) of my STIHL model FS56 weed trimmer is shot. This is a very old machine. STIHL wants $125 for a new pinion set and plus I would need bearings. I cannot justify $200, but the engine runs great. I want to purchase a gear head on EBAY but nothing matches the FS56 model number. Some look like they will work, but I cannot be sure. There are even pinion sets available for much less, but none match the part number exactly. They look the same, and even the part numbers are close, but no match. There is very little information on the web regarding the FS56. This is an odd ball model according to my email exchanges with STIHL directly. They were of no help, and neither are the STIHL dealerships. "Buy a new one!". The machine has a 24.0mm straight tube. Is there another gear head out there that will fit a 24.0 mm tube? Maybe even a Craftsman, Echo, or something. I am quite handy and can do some alterations or make bushings if necessary. Even if I have to dedicate it to a string only. The attached drawing is of the tube interface that I drew. Any help or ideas would be appreciated.