The answer to that question is an emphatic NO! The only way I can think of a valve cover gasket having an effect would be if someone used a LOT of gasket sealer and it got into the valve train and then into the engine oil passages. I didn't use any type of sealer on the last valve cover I replaced and had no leakage at all. That was on my old Grand Caravan. Of course, I'm one for following torque specs too and not over tightening things. The engineers have the torque specs for a reason.

the increase in static oil pressure inside the valve cover (leaking vs sealed) would not be enough to affect the head gasket unless someone messed with the head bolts, so no. The valve cover simply constrains the oil to where it needs to stay. Is there a pressure increase as a result of fixing a leaking seal? Sure. Enough to stress out a head gasket. Quite doubtful IMHO.

My engine has overheated so badly multiple times. There's been oil in the coolant so that's what the mystery is. The fact there's no serious leak is amazing!

i would suggest you do a coolant system leak test to see if it holds pressure. You can usually rent one from your local auto parts store.

I agree with scoffman. I think I paid a $150 deposit on the pressure tester at Autozone last year, but you get that money back when you return it. You don't return it? You bought it.

does the aux cooling fan behind the radiator ever come on? My guess is no.
Per your other thread where we are discussing the ects, your ects has likely failed and if so the aux fan will never turn on and you will indeed overheat.

That's my guess anyway. try the ects and connector.

It does not and has not been able to full pressure for years. I still need to replace the original heater hoses, and the 2 year old lower radiator hose is leaking from the oil soaking it.

As for the cooling fan, it always comes on at the right time. It never reaches the red zone because the fan starts and the needle drops to cool. The only time the gauge has went to red, was when it went off the charts from no coolant in the system. The fan that day stayed on even after the key was removed because the engine was so hot.

So yes, the fan activates normally when it's supposed to, and it always has. When I am driving I keep checking all the gauges and when I see the car is running hot I listen for the fan and then before red it turns on and the temp goes down to a safe zone.

Thinking outside the box maybe, I realized that we do not have full coolant pressure, so a test is just a waste of time because I already know it can't hold full pressure. Now because the oil was in the coolant when the system couldn't maintain full normal coolant pressure, can the lack of full or maybe lack of all pressure in the cooling system allow oil to be introduced through any spot with a open part, such as the thermostat, lower radiator hose, or water pump? (like a crack or anything related)