You definitely need to get that paint off. Then lube it with white grease. I wipe mine clean and put new white grease on it every time. Use lacquer thinner or other similar paint remover. Just be careful and don't let any of it seep into the seal area.
If you have a front PTO, put the lever in that position to allow the rear one to turn. This helps.
The PTO connection for my brush hog is a terrible design. You have to pull back on a collar and seem to have to get the thing at just the right position on the PTO shaft before it'll slide on. Once I get it on, I've learned to also give it a tug back to make sure it's locked. Didn't do this once and had it come off!
I like the design of the PTO connection for my McKissic shredder MUCH better. It has a button that you push to get it unlocked to slide on. It seems to go on any number of positions, too.
On both PTOs, I support the PTO shaft on a tension cord to take the weight of the thing off my arms so they can just concentrate on getting the locking mechanism unlocked and the PTO in the right position without struggling with the weight of it, too.
If you have a movable cover over the PTO shaft, raise it up.
Ralph