Bro, if you want to find ****...you will find it
more you open that engine (yes every gasket will start to leak and will need replacing) more you will find **** (**** FOR YOU because the engine is a NA V6 and it doesn't care about, it will continue to run)
your cougar even likes to smoke a little ..it's an over 20yo car
does it worth to waste time cleaning like perfection/polishing things of a 68cv/liter engine?
this engine is a solid one,
maybe you can do happily 100.000km more with little leaks like that
friendly, stop getting worried and drive it!!!
AND
in the meantime... because i've seen you like to get busy:
buy a 2011 ford fusion/ mercury mylan (THE LAST DESIGN DURATEC V6 3.0) used engine from usa and begin "the costruction" of a future good upgrade, its the cheaper way to rejuvenate your 99 cougar and get REAL HP.
Not the torque curve supply of the fusion, but a peaky one (fault of no possibility of utilise his vvt for us) but with all his 243hp yes, yes the fusion's got 243hp with all stock (so egr,cats,stock filter etc etc).... imagine with some basic tune/exhaust/filter...
The 2009-2011 heads, ports and intake manifold are completely upgraded,
one level over st200, svt, taurus/escape or st220.
like that ...you will drive ...and you will work... in the same time..for something that worth