Oily and carbonized spark-plugs

[aeklo]

I've tried to search the forum for this exact case, but can't find my symptoms explained thoroughly.

So, I'll give it a shot

I have a MB 230 CE w124 '88 4 cyl. with a mileage of 158.000 km, or 98.000 miles.
Cylinder 1 & 2's spark-plugs gets oily (also on the threads), and after some time carbonizes and deposits build up. Cylinder 2 is most badly affected.
Cylinder 3 & 4 has its spark-plugs lightly carbonized.

What has been done the last 500 miles:
-Cylinder 2 ignition lead detected faulty and replaced (0 ohm).
-Replaced rotor and distributor.
-Measured all ignition cables.
-All spark plugs replaced.
-Replaced cyl 1 & 2 plugs once more do to build-ups.
-Replaced valve seals (on top of valve rods).
-Cylinder compression measured to 154, 167, 158 & 159 PSI indicating in fact that #2 cylinder (w/ most oil) has the highest compression.
-Oil changed at 10.000km (6.200miles) intervalls using semi-synthetic oil 10-40.

Now, I turn to you experts out there! What is wrong with my engine?

Would the GM X66 "wonder-solution" help in this case?
Some mechanic recommended some "Omega Oil Additive" that would do miracles... Any info on this?

Where could this oil be coming from?
Wouldn't the normal compression measurings indicate that the piston "seals" are tight? I guess that will prevent oil from a defective piston oil seal reaching the cylinder!?

Could oil get from any of the oil channels of the head without losing compression?

What about valve "steerings"?

And, finally, isn't this a bit early for a engine overhaul? Considering the 98.000 mileage?

Will be _very_ thankfull for any tips!!
Seems a faulty decision here might cost me som huge $$$

Anders Eklo - Norway.