I am rebuilding my 4 speed all synchro gearbox (EJ15734) and am a little confused about the laygear. I need to replace it as it didn't survive the last owner filling the gearbox with water. :-) My issue is that the laygear that i have is stamped as part #c20500 and all i can find on line are C20712 gears. Are these interchangeable? I think they have a different number of teeth on the big gear. The c20500 that i have has 28 teeth on the large end. The c20712 appears to have 29 teeth (looking at pictures of it). If these are not compatible, does anyone know where i can get a replacement or do i have to replace the front shaft (i.e. 4th gear)?