[T2] any precautions with the fan-alternator retaining nut?

[Robert Mann]

       Those familiar with the T1 'upright' engine would have no difficulty
identifying the 32 mm nut which fell from my '73 T2 yesterday  -
conveniently, just in front of my garage door.
       I thought we had installed the alternator firmly after ascertaining
that approx half of the slip-rings had worn away.  Evidently not  ...
       Any insights please on special precautions to keep it in place?

Robt Mann
'73 1600dp Devon