Manuals:
You must have current service manuals to do any (including
preventative)
maintenance on your bird. That includes all service letters. A few
pilots grumbled that certain companies will not send the service
letters
to the owners. The Safety Inspector said that didn't matter. Missing
a
service letter makes the manual out of date and unusable.

Well ,I hate to bust the FAA's bubble but,For a part 91
operator,Service letters are NOT part of the maintenance manual. Nor
are mandatory service bulletins.. joe