x2 on making sure the allen is firmly and squarely set into the bolt.

as an aside, Stahlwille allen sockets are the best bar none. after rounding out too many allens with Snap-On, Matco, Mac, etc., i eventually ditched them all and replaced them with Stahlwille. the Stahlwille sockets are machined just a little more precisely and that extra bit of snugness makes a big difference. i am in no way affiliated with Stahlwille but they make some fine tools.

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W108
W116
FJ60