Burning oil - diagnostic techniques

[arcon]

okay, I have two cars with this issue... a 1.4L Zetec SE and a 1.8 (I think it is) duratorq HE. Both burning oil. Both on heavy acceleration, but the zetec also on idle and worse on acceleration.
The former (zetec) has had new valve stem seals, no difference.

The I guess it either comes down to valve guides or piston rings...

So (Q1) are there any in-car diagnostic techniques that can determine which?

Compression tests on both show compression is within 10% of each other and is not down. Making it a wet compression test makes no difference to the results.


Leading on to the question (Q2) if it was caused by the oil control ring, would compression usually be down also?


If one of the engines was removed... (Q3) what actually am I looking for when removing a piston and the valves on one of the cylinders to determine which is the cause?

Thanks