Valve cover, or Cylinder Head Leak

Been searching for vacuum leaks for awhile and found a big one.  Used the pressure test by the homemade fitting for the TIP, and found the leak.  The little half moon gasket piece is missing from the head back at the firewall right beside the coolant temp sensors.  How can this happen, and am I lucky and this is only the valve cover or am I looking at Head removal?  Any shortcuts to fix?  For reference I've had the P1128 code.

2000 A4 1.8 Q 120,000 miles

i believe the half moon gasket is the cam sensor gasket. not sure if you need to remove the valve cover for that though but i don't think so

Yes, cam tensioner gasket.  You have to remove the valve cover gasket and do both at the same time.  Neiter is hard to do.  First timers take about 3 hours and with some experience takes about 1.5hours

Hey Cincy, do I need that cam chain compression tool just to do the gaskets, or do I only need a cover gasket and cam tensioner gasket?

Actually you can do it without the special tool if you undo the 3(?) hex bolt and slide in the new gaskets.  When i did the passat, we would of been done an hour sooner if we did that first.   Not to mention that its way easier that way.  I know there is a how to on passatworld that has that method.  Im sure there is one on here or audizine also

That half moon gasket is not missing, but it is one half inch deep, or recessed, from the surface.  I read that somewhere else on this forum so I had to check.  But, it was passing air big time when I pressurized it earlier, so it is somehow connected to the boost system.  Stupid question, but should there be any pressure or vacuum up there?  Certainly there is oil up there, and there will be some oil leakage up there, but will there be vacuum sucking in "unmetered" air, too?

You basically have a huge air leak in the head.  Fix it asap