416 oil leak

Sounds like youve got it figured.Also sounds like your engine could use more ventilation, or less blowby. Blowby can be measured.
At high rpm the pcv system is defeated, and the pressure goes out, or is supposed to go out, the breather. If there is insufficient venting for the amount of blowby, the pressure will get out anyway/anywhere it can.
The chinawalls arent usually the first places to fail.
Usually the dipstick blows out. Or the breathers pop out.Or the valve cover gaskets seep.
You could plumb in a pressure gauge, viewable from the cabin and see whats going on, or have the blowby measured.
Id hate for you to replace the endseals, and have it happen all over.