It sound like you've done all you can as far as adjustments go. It may be time to take in into a shop, or if you feel comfortable, take a look under the hood. You may find a a spring loose, or the remnants of a broken part. Or it could be a matter of cleaning and changing the grease, which over time becomes tacky and could be making something stick instead of sliding. I've done it before, on electronic equipment with moving parts,using some alcohol (91%) and Q-tips. I believe you'll see a white grease, as I say over time, tends to make things stick rather slide freely.