On my M104 I used The Right Stuff based on recommendation of a guy who has built a lot of AMG 104's, that plus nobody sells the Loctite 59XX products around here. He says no matter which sealant you use, the secret is in the preparation. An interesting side comment he made was to just plan on this job being on a 4-year PM cycle, like the head gasket. Drive it 4 years, do the head gasket and timing covers. He also said another thing he does is to apply the sealant, set the covers in place, run the bolts up just snug and then let it sit overnight, then torque the bolts to spec the next day.

After researching this for months, I have come to the conclusion that the realistic issue here is that this is a hopeless sealing job/physical impossibility to expect leak-free performance over the long term. There are just too many metal parts and unequal joints moving around down there, too much temperature cycling, too much exposure to oil for any seal to last any length of time.

There is a sign on the wall in my local import parts shop that says 'If It's German, It Leaks'.