There are many posts that mention cleaning the vent while doing axle work. Thanks to this forum for hosting that information. I would not have known about it if I had not read about about it on this forum. I found and cleaned it on my 1949 2R5 truck.
Here is a picture of its location. I show it with a bent nail in it.
Here is a picture of its location. I show it with a bent nail in it.