The car'slower intake manifold gasket started leaking coolant into the oil and when I got the manifold off, I saw this






The passage in the lower picis chock full of this oily gunk and the upper manifold under the plenum has a lot of oil in it as well, which appears to be connected. I read somewhere that this may indicate a need to replace the valve guide seals. Is this correct? The car is running well otherwise.

 

Leaking valve seals and/or loose guides shouldn't cause the whole runner to get built up with carbon like that, but I guess it is possible... A better indication would be the buildup on the back of the valve, but the only real way to take a look at this would be to pull the heads and if you were going to go that far, you might as well get them refurbished anyhow.

 

Could it be leaky valves or bad rings instead? Or, if it's running well could it just be cleaned up?

I had a problem with the fuel pressure regulator goingouta while back where it was getting horrible gas mileage - and I know the previous owner was running low quality gas through it for quite a while. Do you think these could have had an effect on it or caused it?

Would a leak down test be worthwhile? I'd like to avoid pulling the heads unless it's really necessaryof course.