Motorhome hinge corrosion on habitation door

Forgive me if there's already a thread open on this subject, and point me there!

One of the 3 hinges on the external door to my 1995 Autocruise StarSpirit has become VERY stiff, to the point that I'm sure that the mounting in the door frame will break before long. I've tried WD40 and 3-in-1 to no effect. I'm told that replacement hinges are not available anymore, and that stiffness is due to corrosion between the dissimilar metals used in the hinge and pin. Is it possible to dismantle these hinges and make a repair? If not can anyone suggest a source for replacement please?

Thanks!