After having my balancer come off twice on my 300SD...I did the re-drill and added 2 extra holes...using tapered roller bearings. This was 15K ago, and I still check the crank bolt at least once a month. I just went on a 3k Trip with no problems. Good luck!

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1983 300SD 343K everyday car
1983 300SD 285K from junk yard-tooks parts from deer car- runs great. Brothers car.
1984 300SD parts car-Hit deer
1979 300D 175K non-turbo "Doctor"
1979 300d parts car