There is a piece of foam inside that has deteriorated / disintegrated. Take the bottom off and look for remnants of where this foam piece once was . You can then clean it and glue a new piece of foam rubber on and it will return all the way. Sorry for not being more descriptive , but when you go in and examine the tone arm automation bits and pieces , the part I'm referring to will be obvious. In the mean time I'll try to find a previous thread to link to.
Found it
here post #14 and #19 have good pics from service manual.