You do ROCK and are absolutely right about that , the trans dip stick is "somewhat" vented by not making a tight seal to the filler tube ,so as to act as an air vent. But if a "leak back" accurse draining the torque convertor in to the trans case it will fill up the case blocking the filler tube bottom area and cause it's seal to leak BUT if the seal don't leak and let the oil out =now there is no vent any more trapping the air inside which in turn raises the fluid level as it drains back. Then when you start the engine the trapped AIR's only way out is up through the filler tube along with any trans fluid in it.
In 58 up GM added a VENT L/S in the rear main case area the size of a quarter.And again your right GM had a call back or (fix-it) to help this problem as you stated by drilling and adding a vent (but in the rear housing and not the main case area as the 58 up were. It helped but not %100 because of the rear pump blocking and it being lower then the top case area.
Many old farts (like me)just drilled a 1/4 hole at the top main case to solve the problem using some grease to catch the filing and added a vent cap.
This would be a good Article for a NCRS guy to send to the Restorer , towards some award NCRS gives out. I'v heard many ask about this problem on the board and hope you all understand how I put it.
In 58 up GM added a VENT L/S in the rear main case area the size of a quarter.And again your right GM had a call back or (fix-it) to help this problem as you stated by drilling and adding a vent (but in the rear housing and not the main case area as the 58 up were. It helped but not %100 because of the rear pump blocking and it being lower then the top case area.
Many old farts (like me)just drilled a 1/4 hole at the top main case to solve the problem using some grease to catch the filing and added a vent cap.
This would be a good Article for a NCRS guy to send to the Restorer , towards some award NCRS gives out. I'v heard many ask about this problem on the board and hope you all understand how I put it.