Well, I must say, I'm deeply hurt (not) that no one answered my question. Your punishment, a follow up post.
I gave up and called a specialty muffler shop the dealer recommended. They found the forward down pipe was cracked near the manifold. They used a very high tech precision instrument to locate the leak...a rubber hose.
Anyway, they fixed (welded) the crack and I'm purring smooth and quiet. The reason for the follow up is, I'm not sure it's necessary to take the exhaust pipe loose to remove the manifold. At least not on a '90 300SE.
This might save someone searching the subject a little time and money.
91 300E 120K
90 300SE 275K (sold)
92 BMW 525iM 120K
90 BMW 525iA 175K
85 300D 175K (sold)
84 300SD 245K (sold)