The T-400 speed-O housings are divided into 36-39 and the 40-43 tooth designs.
The T-400 stem of the plastic gear is a different diameter for each housing tooth count design. You can not interchange the gears between housings. A 44 tooth gear will not fit a T-400 housing for 36-39 tooth gear or the other way around.
I suggest you verify the correct parts are on the T-400 output shaft, then verify the driven gear and housing. I had a fellow a few years ago , trying to install speed-O housing for a torque flight into a T-400.
Dont worry how old you are... it is the mileage on your body that adds up.