Hi, glad you have found a replacement, but do you need it? The ZF box was/is found in the old CF Bedford, I've been told to look for the 'big' input shaft, that's the one. Most rear wheel drive gearboxes are 1:1 in 4th or 'top' so ratio is not an issue. Chevy boxes ues 3 speed, but 3rd is 1:1 !! The great thing about running this or indeed any box of rear wheel drive cars/vans is that no drive is transmitted through gears. The drive is "straight through" by locking input shaft to output (main) shaft. What this means is no teeth transmit torque when the car is racing. Doud Nash type boxes use gear teeth to transmit the torque, and hence the reason for their 'occasional' failures. Using an FG/LD axle it is possible to race on most tracks, but the engine is not always in it's most efficient torque range. If you use a transit rear axle it is almost impossible to work with 1:1 gearbox due to the final drive reduction and a 'nash' box will be required! To be honest it sounds more like a problem with the selector hub and spring/detent mechanism, so don't throw it away yet!! Regards!