That is almost certainly not from a valve cover gasket leak. That is probably just condensation or something similar.

Valve cover gasket leaks will present as oil leaks from the valve cover downwards. If leaking onto the exhaust it will also be accompanied by smoking.


Per your original post, I also wouldn't pre-emptively replace working O2 sensors. Really no need to do so. O2 sensors out of the box have a surprisingly high failure rate, and unless something fouls them (welding an exhaust without removing them, spraying the sensor or plug in cleaner which ruins the clean air reference intake, burning excessive oil fouling them) then they can last for, in most cases, the life of the engine.