I used lock-tight on mine also. Not much, but just a dab. I also torqued it by feel. It actually came loose once after I didn't tighten enough and caused the fan to start hitting the tensoner.

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1995 E420 152k
1991 300D 2.5 348116 daily driver
1992 300E 2.6 196k-work in progress(head gasket)
2002 BMW 745Li 93k