Try pedaling a little "knock-kneed," where the inside of your knee nearly scrapes the top tube. I heard about this after experiencing some pain about 10 years ago, and it cleared it up. Now I pedal that way unconsciously. Never any more knee pain -- and I'm 60.
Also, take advantage of your gears. Use a faster cadence and lower pressure on the cranks.
FWIW, I think glucosamine is a scam.