what seems to be the reasoning for not putting the vent in the rear of the case?, for years it was the accepted practice to do just that and now it's appears to be taboo, I have always put the vent in the rear of the case and plugged the front one.

But you did that with a brake, I never put it
the rear if NOT using a brake

I thought they ment in any combination, maybe I mis undestood.

I don't know why it went out of fashion. They're saying Cope and Tranzact don't want it done. I don't know the reason. All I know is I've done it for years on units with a brake from Griner and Protrans with no issues. Perhaps they stopped with putting the small hole in the high drum which I understand is the main reason for moving it. I'd like to hear from one of them for a clarification.

I know in the (Carl Monrow) 727 book it says to
move it and I did

My last trans was built by A&A. It was the only trans I had with the vent moved to the rear, and the only trans I had that leaked from a vent. I ended up running a nylon tube up to the dipstick to prevent the leak from oiling down the car on a heavy pass. Hardened shafts-so no governor. Just didn't work for my combo. The tube solved the problem so I guess it turned out fine in the end.
I could see how a drilled drum would cause an issue with the pump located vent. Maybe they vent the drum differently now so relocation isn't needed?

I am not running a brake. When I posted my original response a brake was not mentioned by OP.

I've had mine apart 2 times for inspection in the last 3 years. Now has 350 passes in a 9.0 car without a brake. Vent is in the back. It is in the suggested location. Tube to a catch can at the rear bumper. Catch can has never leaked or been emptied. Both times the inside of the bell housing has been completely dry. It hasn't had the pump seal replaced since originally built.
Doug

pipe threads will wedge the surrounding material with the fitting, and there is a recommended wall thickness surrounding the fitting for different materials, but i don't know where my chart for that is. if you have one side of the surrounding material much closer to the edge of the hole [think of a very offset hole], the wedge effect will concentrate on the "thin" side more than the "thick" side, promoting a crack to form. also, most seem to have a tendency to crank on pipe threads so they don't leak.

The vent doesn't have to be threaded, I have one that I think came with my brake that is push in.

I don't drill and tap. If I did, I would use 1/16NPT. I use these.

I run one of Cope's transbrake valve bodys and don't honestly remember John telling me to NOT put the vent in the rear, when I put the new billet steel high gear drum in I drilled the piston which pushes the fluid toward the rear,, with that said I have not had a issue from the rear vent.

You can also use other materials to ensure that the alloy material is essential in this case. I once put a panel for myself and made a mistake with the materials. So it did not last a year, as it broke and began to rattle. So now I constantly look at what is where. To then know what is better to take products for yourself and your loved ones. Recently, there was a question about the air conditioner and its choice of truth. Who not to ask everyone complains about something? I even started to think about not taking it at all.