GU & I don't like what I see....

The 3lt TD has been somewhat hard to start these past few months & I finally got some time to have a look. It's early '92 model with 83K on the clock (young for an oiler)

I thought it may have been the glow plugs but the power supply tested OK, so I lifted off the intercooler etc to test individual plugs. Here is what I have found without the need to remove the glowplugs...

The throttle box body which bolts to the inlet manifold splits from one large inlet apeture into 2 smaller outlets one of which is called the "air control actuator" (aca), the aca port is heavily coated with oil (or fuel) soaked sticky carbon deposit the other inlet port is clean.

This is all on the inlet side which should (IMhumbleO) only exhibit nice clean polished ports, and whilst this aca port is where the heaviest build up is, the intercooler and air pipes from the turbo all show a light oily coating without signs of carbon.

My first reaction is that I might be looking at a burnt out inlet valve which is strange as it usually is the outlets that are prone to burn, maybe some head distortion could be a cause.

Have we got a diesel expert on the panel with an opinion or diagnosis & possible remedy.
I'm just trying to think this through to make sure I get the best answer to what might be an expensive find.