8-12 oz on my E-38
Ted, the trans on my E-38 Universal M-40 (5432) only took 8 to 12 oz of fluid. Do you really have a M-50? Anyway, changing the trans oil is a real PITA - probably my least favorite fall winterization task.
It wasn't that bad to suck out with a tube leading to a pump, but getting it back in without spilling took a funnel hooked up to a long piece of hose to avoid making a mess. I would put in an 8 oz cup all at once, then one oz at a time till it registered full. And by the way, a trick I was shown to help visualize the level on the trans dip stick is to roll it across a clean white paper towel. That leaves a stain that you can see, while the level itself on the oily trans dip stick tends to be invisibile.