I finally heard back from Mahle:
Thank you for your interest in MAHLE fuel filters.
KL 736/1D initial efficiency is 91% at 4 micron.
Kind regards,
Lisa Levra
MAHLE Aftermarket Inc.
Product Management (MND)
I am not pleased that 9% of contaminants are getting into my system so I am going to go with a 2 stage filter setup as recommended by diesel engine makers.
Right now I am seriously considering this one;
https://www.glacierdieselpower.com/i...f=category:111