The story continues....
I tore everything apart again today, and this is what it looked like (and possibly my thoughts on what's going on):
Here's the breather hose to airbox connection, and the airbox drain. Nothing looks amiss here.
Here's the breather tube to valve cover connection.
There were no kinks in the breather tube.
Here's the breather tube fitting with the breather tube detached.
This is the end of the breather tube that connects to the valve cover
Coil sticks 1 and 2.
Coil Stick 1, removed from the spark plug well.
Spark Plug Well 1. You can see the oil seeping past the tube seal.
Here's Coil Stick 1. You can see that the end is pretty soaked with oil.
Here's Coil Stick 2, in the same condition.
Here's Coil Stick 3, in the same condition.
Just like when I changed the spark plugs, spark plug wells 1, 2 and 3 had oil in them. Based on how high up the coil stick the oil appears, it looked to me like the oil was leaking down onto the coil sticks from about where the tube seals are located. I couldn't see clearly into spark plug wells 2 and 3 to be sure that the oil was actually coming from the tube seals, but the location of the oil on the coil sticks makes me think that the oil's coming from the same place as it is in Spark Plug Well 1.
I didn't pull Spark Plug 4; I didn't think there'd be any point. It was dry last time, and even if it was wet now, it doesn't really change anything.
I looked really closely at the valve cover from as many angles as I could see, and I couldn't see any damage anywhere on it. There's no damage anywhere on the cylinder head either, or the crankcase.
I didn't drain the oil, but I can see the oil through the sight glass, and it doesn't have that chocolate milk look that happens when a head gasket blows and coolant gets in the oil. There's no coolant loss that I can tell.
Here's what I think is happening:
I believe that the breather tube fits into a PCV valve on top the valve cover. The PCV valve, it it's like a car, is a one way valve that vents pressure inside the engine but doesn't allow anything to enter through the valve. If the valve is stuck in the closed position, then the pressure can't vent through the valve and has to go somewhere else. That might explain why three of the tube seals began to leak oil, and why a secondary leak may have later appeared on the left front part of the valve cover gasket; the internal pressure breached the tube seals first, and the continued extra pressure in the head eventually forced oil out the front also.
I looked on line at Rocky Mountain ATV, and I don't see the vent on top the valve cover listed as a separate part. Is that vent tube a PCV valve? And if it is, can it be replaced, or is it integrated into the valve cover and you have to replace the whole part? Is there any way to test a PCV valve while the valve cover is still in place?
I got my new valve cover gasket and rubber mounts today. I'll probably have it installed regardless, since the old one has already leaked.
I didn't want to run the bike again after I finished to look for a leak, because I don't want to to take a chance on fouling the plugs and have to take everything apart a third time so I can ride the bike to the shop.
So, anyone have an opinion on my theory, or a different theory of what's happening?