2001 Vauxhall Corsa yellow gunge in rocker cover

Engine Mechanical problem
2001 Vauxhall Corsa Engine Size unknown Front Wheel Drive Manual 75000 miles

Hello,

The engine is a three cylinder 1.0 litre eco petrol version.

The car has been sounding very rough. It keeps losing oil at a high rate, but there is no sign of it on the road under the car. There is a lot of oil around what looks like some sort of sensor on the front of the head - on the left side as you look at the engine(it has a lead coming out of it). I took the rocker cover off and there are two pipes that run from the back of the rocker cover (on the right as you look at the engine) the larger of the two runs up to the housing that sits above the throttle body (which I assume is meant to only carry air). Both of the pipes were virtually blocked by a yellow (kind of tan coloured) gunge that I can't understand where it is coming from.

Also when I opened the throttle valve there was a build up of black greasy gunge on the under side of it, so presumably there is a load of it down inside the throttle body. I took the spark plugs out and there was a build up of black carbon deposits on each of them, which I understand means that it is running with a rich mixture.

Any ideas what the yellow gunge or the black gunge might be and what I could do to try and sort it out?

many thanks for any help you can give,

James