Yeah, easy fix. The mechanism is spring tensioned, and the lever arm very likely has oil on it. If you search the web, you'll find that it is a very normal failure for the age of the lenses.

To fix it yourself, take the screws off the rear mount. You'll see the mechanism and spring loading. Take the lever and spring off, clean it all up with lighter fluid (naptha) and put it back together. Some suggest leaving it dry; you can also use a tiny amount of shutter oil.