I was somewhat concerned about the tar like build up on my 300D intake (near the EGR valve) so I did a search of www.mbz.org (when it was alive).

The diesel Doktor himself said that of all the cases where people had gone to the trouble of cleaning out the intake manifold, he had not heard of one case where performance was improved.

So unless you have an extreme case, I would leave the manifold alone, and maybe just "fix" the EGR valve.

Joe