If it were me I'd change it, if that one cup is turning it's going to wear your yoke so that a new cup won't stay tight. Crosses are cheap yokes are not! That cross is done anyway even tho it feels tight, dollars-to-donuts says its dry as a popcorn ____t and due to become very very loose sometime in the very near future, and you do not want a drive shaft coming appart and crashing round an round an round undernieth nelly bell whilst you try to change lanes and get her off to the side into the emergency lane then try to revive the missus who's just had a cardiac arrest. You get the picture I'm sure!!That being said, that half of of the cross is easy to check by removeing the two straps and attempting to rotate the cups. You'll know right away if it's dry. Quite offten for some reason one side will be short of grease and siesed-up while all the rest of the cups can be well lubed and apparently fine . If you do find that all is well and cups all have grease then for sure clean the recesses and cups and deffinately use a new strap. Then watch it for the next while to make sure it has stopped rotating in your yoke.
Hope my long-winded reply helps.