I've checked for leaks... cant find one, yet.
The valve is creamy coloured, transparent, and looks like a check-valve. It is probably 1/2 inch thick and about 1.5 inch in diameter. There is no noticable force of air in or out of it at idle or at low rev. Could it be a vacuum line with a check valve?
I believe that the crack occured when the belt broke and flopped around under the hood.
If this is an EGR, it is news to me
76 240D - 550K miles
78 300D - 200K+ miles