Classic/Antique Car Repair: 1957 chevy 2 speed powerglide transmission, speed powerglide, dipstick tube

Question
hi
i have a 1957 chevy 210 4 door with a 283 v8 and a two speed powerglide transmission. my problem is the transmission fluid is leaking out of the dip stick tube. this dose not happen each time i drive the car, only sometimes. it will also lose fluid through the dipstick tube when the car has sat awhile and it gets hot outside,but not always.
other than that it runs and shifts fine. do you know what could be causing this?
                      thanks

Answer
If you mean that it is leaking out around the fitting where the dip stick tube enters the oil pan, that has to be a bad gasket at the fitting.

If you mean it is coming all the way up the tube, then I can think of two things.  

The first and most likely is that your vent on the top of the transmission case is plugged with crud.  

The second is that there is some contamination in the transmission fluid that has lowered the boiling point of the fluid from 300 degrees down to 200 or so, this is making the fluid boil up and overflow from the increased pressure in the trans.  You can spot this by inspecting the fluid. If it looks nice and clear, and red, and doesn't smell burnt or show any milky look, then it's probably a plugged vent.

Dick