I just got my hands on a copy of Lycoming Mandatory Service Bulletin 548A.  Apparently four different fuel pump models installed on a everything from 235's through 540's "may not have been manufactured in conformance with acceptable standards".  Pumps purchased from 2-22-2000 through 9-15-2005 may be affected.

I'll be checking mine this weekend.

http://www.lycoming.textron.com/support/publications/maintenancePublications/serviceBulletins/SB548A.pdf

Chris Zavatson
N91CZ
360 std
www.N91CZ.com