I have a leak from #4 cylinder exhaust manifold port on my E200.

I took off the manifold, lost a tea-spoon of O positive in the process, and found it seems to "rock" on the centre ports where it mates against the head.
So when I fit it back, the centre two fit well, but either #1 or #4 do not.
There is about half a millimetre gap at either end where it should bolt down to the head. Is this normal? I've tightened up the nuts to the correct torque but still #4 blows just a tad. I guess if I tightened up #4 first then #1 would blow.

Do I need a new manifold? Or can I get the mating surface machined off from the centre two arms? or should I fit an extra gasket at each end?

Any ideas guys?

E200 Wagon '94 M111 engine. 109k miles