I am installing a new ZF 25 transmission
It has been test run at the factory, and arrived with oil in it
When I unscrewed the dipstick yesterday, there was a hiss of escaping air.
Same again today
Engine has not been run yet, and the ambient temperature has changed by less than 5 degrees since yesterday
I removes the breather. It is hard to blow through it, and sometimes I cannot. It is even herder to suck, although is easier if I wiggle the loose part around

This seems like a blocked breather to me, that will causes oil leaks when the transmission warms up

Any comments?
Is it possible that the gadget relies on engine vibration to wiggle it and let air pass in and out?>
Should it be hard to blow through it?