I had the same problem with my '81 for years, and also had the problem that after a heavy rain it could be very difficult to lock/unlock the doors---I worried I might break the key! What I would STRONGLY recommend you do is simply disconnect the electric motor which triggers the locking mechanism from the lock mechanism/linkage. These electric locks are a mess (badly designed as an afterthought, I suspect), and I finally simply took off the door panel (which is simple as its held on by screws, not wire-type "locks" which never go back correctly) and disconnected the little rod which goes between the electric lock "trigger" mechanism and the lock button/linkage. This can be done by simply prying the rod from the nylon connector with a screwdriver---everything is easily reachable and takes less than 30 seconds. I got a VERY smoothly functioning normal lock action with minimal pressure needed as a result, and these cars are so narrow you can easily reach across and lock/unlock the other door. This will be a major improvement if you do it, and you can always reconnect everything if you want to---but you won't want to.
--Chris Kennedy
Houston, Texas