Canon EF 300mm f/2.8 L IS II USM Lens Service Notice

Canon Inc. has issued a service notice regarding a very small number of Canon EF 300mm f/2.8 L IS II USM Lenses (thirty seven of them).
 
If you own a 300 L IS II with one of the serial numbers listed below, you might notice significant backfocusing when one of the Canon EF 1.4x Extenders (version I, II or III) are also mounted. If this is the case with your lens, contact Canon for corrections to be made.
 
8210000204, 8210000331, 8210000335, 8210000338, 8410000266, 8410000296, 8410000276, 8410000339, 8410000344, 8410000347, 8410000348, 8410000357, 8410000361, 8410000368, 8410000369, 8510000008, 8510000014, 8520000122, 8520000146, 8520000191, 8520000213, 8520000275, 8520000324, 8520000338, 8520000354, 8520000357, 8520000358, 8520000361, 8520000365, 8520000366, 8520000378, 8520000335, 8520000414, 8520000441, 8620000114, 8620000130, 8620000032
 
No reason was given for the source of the problem.