EGR and inlet manifold

Hello all,
I decided to check the intercooler hoses for leaks on my 05 Freelander. I found black oil in the hoses and checked the EGR which was found to be gummed up with a tar like substance. I removed the inlet manifold and was horrified to see how badly the ports on both the head and manifold were gummed up with this tar. The round ports were thick with soot/carbon.
I would like to ask for someone to explain the function of the EGR and although the valve does now open and close it seems to take a fair bit of effort to push against the spring to open. I just can't see that small diaphragm pulling it off the seat.
Also I would like to ask for an explanation on the intake manifold ports i.e why is there 8 ports and the fact that the square ports being tarred up and the round ports being sooted up.
Cheers
BD

There are lots of posts on egr. Its function is to reduce combustion temp and therefore the level of oxides of nitrogen in the exhaust gases.
The vacuum chamber is very powerful and obviously designed to cope with the return spring pressure however as stated in various previous posts it's best to disable egr by removing and blocking the vac pipe to prevent your hard work cleaning the inlet being a waste of time.

8 inlet ports due to 8 inlet valves.

can't really offer an explanation on why the square ports have more tar other than the effect of the differing materials/temperatures or perhaps more of the oil drops out toward the lower ports.

Thanks chaser,
8 ports for 8 valves makes sense.
I just did not expect to find the inlet side of an engine so grotty and the round ports look more like a sooty exhaust.
I'll hoover them out.
I really should buy a workshop manual as I've never worked on a diesel engined car before. Only petrol in the past.
Now where is the engine breather filter fitted?
Cheers
BD