I just saw a thread on hummernetwork about this item -- they said you could take it off, clean it out, and reinstall it.
Thread was titled "What is this?" and had some updates this week. Quotes below:
I ordered one from Hummer Parts Guy. I think it was $37.50 plus shipping. You can get one from Napa as well.
*
Pull up on the tuna can (it will pop right out of the black tube its on top of). Clean the inside with a rag, there will be black sludge in there. Then pop it back on. There's no filter, you just clean it out with a paper towel.
_________________
GeneseeMtn
97.5 OT & M101A2 Trailer
Functional Excellence in the Off Road Environment
*
From the Diesel Page:
It is virtually an open hole (1") for the fumes from the crank area to get sucked up into the intake manifold. In the event of a huge vacuum in the intake manfold like say a completely closed intake (sucked in a seagull or a coon...) then the diaphragm is supposed to close off to prevent the vacuum from sucking up crank oil and causing a runaway engine.