You're talking about an early S30 - 1970-1976, right? Not a '77-'78? The rotating mechanism in the earlies can get sticky over the years and the grease turns solid. A temporary fix is to lube the rotating mechanism on the outside of the door with some spray lube. Overdo it - turn by hand and release until it rotates smoothly and easily.
The real fix is to take apart the door, remove the entire mechanism to completely clean and re-lube it before re-installing...