Sounds to me like it might be a failure to comply with AD 98-02-08,

SUMMARY: This amendment adopts a new airworthiness directive (AD), applicable to
certain Textron Lycoming 320 and 360 series reciprocating engines, that requires
visual inspections of the inside diameter (ID) of the crankshaft for corrosion
pits, and if corrosion pits are found during this inspection, prior to further
flight, performing a magnetic particle inspection (MPI) or fluorescent penetrant
inspection (FPI) of the ID for cracks. In addition, this AD requires reporting
findings of inspections to the FAA. Finally, terminating action to the
inspections of this AD is the application of a preventive treatment coating on
non-corroded crankshafts to prevent corrosion. This amendment is prompted by
reports of cracks in crankshafts originating from corrosion pits in the ID. The
actions specified by this AD are intended to prevent crankshaft failure, which
can result in engine failure, propeller separation, forced landing, and possible
damage to the aircraft. DATES: Effective March 30, 1998.

Demonick