Larry, I agree it's probably not necessary to use sealant on the bolt threads of the upper cover. But an MB mechanic recommended to me years ago to seal the lower driver-side bolt because the threaded hole was open to the engine crankcase area. Assumably oil could migrate through the threads and down the bolt and out around the bolt head. Seems unlikely that it could happen, but then it takes just a second to dab sealant on the bolt threads,
so I always do it. The factory manual does not mention this, so it's probably overkill.

DG