Is it possible on R53 to have oil leak from the camshafts area into the combustion chamber through the valve guides?

I'd think it's not possible, since at any time the pressure is higher engine side than camshafts side (exhaust phase because of the explosion pressure, and intake phase because of the supercharger pressure).

 

Yes. Pressure in the cylinder is not always high and crankcase pressure is not always low.

(No real time display of my JCW's intake manifold pressure, but I have thi with my Hellcat (which has a supercharged V8 engine) and the Hellcat engine runs with low pressure in the intake system quite often. Only with more throttle does the supercharger make boost and pressure in the intake goes over atmosphere.)

At idle the intake is under low pressure and this can pull oil past the valve stem seals and through the valve stem/guide.

The seals and stems/guides have to be pretty bad for any real amount of oil to get through them.

If the engine appears to be using oil more likely the oil is from oil vapor in the crankcase -- OHC engines generate considerable oil vapor because of the amount of oil that is supplied to the cam/lifters/other hardware (like cam chains) -- and if the air oil separator is not very good it can let through a substantial amount of oil vapor which over time represents well, oil, lost oil.

Why do you ask?

 

Oil seeping past the valve guides has be a proverbial sooner or later engine wear ever since there is valves. The guide seals are designed to meter oil for the valve stem and guide so they don't fuse together as one. As the engine ages, the seals hardens. Typically the guide's ID also get larger, and the valves begin to wobble, and more and more oil get pass the guides. The burnt oil deposit on the valve grows and you know the rest of the story.

Evidently the valve guide seals on our engines last quite long, I have been told recently. The Prince engines have horrible carbon deposit on the valves even at very low mileage.

 

I have the head off the engine for replacing the gasket and I was considering changing the valve guides too..