I replaced my upper timing cover gasket a couple years ago and it is still nice and dry with no leaks. It's not a difficult job if you take it slow. The gasket itself is a u shaped piece that fits between the upper and lower timing covers. The rest of the assembly is sealed only with the special MBZ sealant (I bought it from fastlane). You will also need a new cam seal if I recall correctly.

To be successful you need to really clean the mating surfaces well. I scraped off all the old sealant and then cleaned the surfaces with lacquer thinner to remove any oil residue. Pay particular attention to the bottom corners, between the upper and lower cover, where leaks are likely to appear. There is a crevass that will leak if you don't get it absolutely clean. I used a sharp scribe to clean all the gunk out so the new sealant can do its job.

John