Zf63 v drives holding air psi

Hello all!
I changed the fluid and filters in both of my 2002 (340) zf 63 v drives a couple if weeks ago. Since then, I’ve put about 4-5 hours on them.
I went to check the fluid levels thus weekend and when I unscrewed the dipsticks, air pressure was present. Quite a bit of air pressure hissing while I unscrewed the dipsticks. The levels were fine but I am wondering if I have a venting issue?
Thanks,
Jim Crews

Mine did that also. Eagerly waiting on the answer.

That's normal. It's not pressure, it's a vacuum. So when you open the stick, just be sure its clean around the outside as it will suck pretty hard for a moment.
There is a vent on the top of the tranny, it blows out the air when the ATF gets warmer, expansion. Then holds that vacuum until you open the dipstick.
If the air can't bleed out, then seals would blow out over time.
If its blowing air out the dip stick, then yes you have a venting problem and needs attention before you run again.

Very good information!
Thanks!