I have never done an M104 head R&R, but I have done the M103. These engines come apart and go back together very well. I find on the M103 it is better to leave the intake manifold in place and remove the head without it. I have been told by an experienced MB dealer tech that the M104 is better done leaving the manifold attached to the head.

Hopefully you won't have to find out the best way to do a cyl head job. Don't panic until you locate the leak.