Internal drag within the mechanism can compound a dirty mast problem. Also, if the mast has a bend in it, that can crimp it's style.
Might be worth opening up the mechanism for a clean and lube.

Of course, for the labor involved (while you are at it), you might consider replacing the mast. These are just $29 from our sponsor.
Not a tough job, unless access is a pain in your wagon.

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1986 300E 5-Speed 240k mi.