Remember what scares the piss out of the big guys, social media! Use facebook to your advantage and if they wont budge, ask if they have a facebook account because you want to leave some feedback.
Bingo. Coming right out and saying "give me free stuff or I'll go to the interwebs" has about a 10% success rate. But hinting at it along the lines of "I'll have to solicit advice from some of the forums to see if my experience is consistent with other's" will often get them to mobilize their efforts to keep bad press from being generated. I've also had luck with "if you're not willing to fix it, there are a few vendors who have offered to replace your parts with theirs so long as I send them the failed ones". That will often make them go bug eyed - they'll hate you, but might be willing to budge at that point. No one likes the competition to have marketing ammunition.
In any case, letting them off the hook helps no one. Not the end user, not any one else, since they'll just continue to put the squeeze on and do even less each time until everyone is just wiling to live with new cams every 100 miles.