You'll need a gasket for both sides (ends?) of the manifold, where it attaches to the head and where it attaches to the crossover pipe. While you are at it you should replace the plastic clips that hold the injection pipes to the manifold. You'll probably break most of them taking it apart and it's not unheard off for the injection pipes to wear through the sides if they are allowed to vibrate due to them not being clipped down.

PEH: 4 out of 6 of the 603 engine glow plugs are virtually unreachable without removing the intake. This may be one time where it pays to at least replace all of those 4.

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold