New Holland 469 Sickle Bushing question

I've got a well worn 469 haybine that seems to be eating sickle bushings. I'm only getting about 30 acres to a bushing. It doesn't seem to matter if it's a new bar with new knives or an old one with dull knives. It cuts fine and doesn't plug or anything, just wondered if there was some adjustments or other parts that maybe causing them to go out so soon. Any insight would be greatly appreciated.

New Holland 469 Sickle Bushing question