I banged my knee a few years ago, and ironically sailing and hiking made it feel better. I guess it was some sort of stretch therapy.
When you aren't sailing, are you wearing any sort of brace? I wore one that had side support hinges for about a year. That took a lot of the strain off my kneecap and allowed it to heel. Unfortunately I think I lost some muscle mass on my inner leg which I doubt I will ever recover.
I can sail and bike, but running seems to be out. Well, the other knee hurts when I run too. Getting old sucks.