not to be contrary here but sealants have come a long way since your old tube of blue permatex (had one in my toolbox that was 15 yrs old). quite a few manufacturers now use sealants like permatex "Right Stuff" and the MB approved loctite 5900, even on valve cover gaskets. the newer sealants are O2 sensor safe. you should specifically check the packaging for this if you plan to use it.
my last car was a Passat with the Audi V6. it had a pesky valve cover gasket leak - the dealer changed the gasket 4 times and never resolved the problem, even with a factory rep supervising the repair. i maintain it had to do with the design of the valve cover because it had curved surfaces to seal unlike traditional designs which just lay flat on the head. i was ready to seal it myself with Permatex "Right Stuff" until i decided to just give it up until the next car. the last year i had it, my engine bay was consantly smoking with burnt oil...
1993 300e-2.8 - gone now <sigh>
"Do not adjust your mind, it's reality that's malfunctioning"