Hi Klunk. I actually got the gears last Friday. The tooth size matched the originals so i only used the smaller motor gear. The gear has a 4mm bore and my motor shaft is 3.2mm, so i also bought some 4mm outer diameter thin walled brass tube, which i carefully drilled out to 3.2mm with a drill bit, and also put a hole in the side for the grub screw to go through to bite directly on the motor shaft. The brass insert on the new gear was too long so i cut it about 4mm shorter, drilled and tapped another hole for a 3mm thread closer to the gear for the grub screw. Assembled all and bench tested ok. There is a slight gap as the new gear from technobots is a shade smaller in diameter than the graupner one, but if it becomes a problem i can elongate the holes in the gearbox plate to move the motor down towards the shaft. On water testing will have to wait a little longer. The gear ratio is slightly as there is one tooth less on the motor gear than on the graupner unit, 15 as opposed to 16. Not sure what effect this will have in practice (slower acceleration, touch more speed, or too much load?). Will update after a sea trial.