1996 E300D Intake valve seat/sealing issues?

[RyanCooper]

So i've had this car a while now and have been replacing lots of neglected maintenance items (like all the plastic fuel lines, the main fuel feed/return lines under the intake, all the breather parts, delivery valve seals etc) and noticed the first time i ran it with the intake off, it makes a popping sound like air leaking past a valve.

put my hand up to the ports and sure enough i feel air pushing out of the second intake valve on cyl #1. at first i assumed this was due to carbon buildup, but its actually not near as bad as i thought or others i've seen, or even other cylinders that aren't doing this. i read about valve seat recession issues on early 606's? but everyone says they've never heard of it/or its on the rear most cylinders due to lack of cooling. but this is cylinder 1 and to my knowledge this engine has never been overheated.. idk what to do? it doesn't misfire (at least yet) but im worried about it since i had plans for this car...