Based only on what I've read on this issue (and not on first hand experience) I'd agree with David and Pherdinand that the problem is a result of improper reassembly. (The observation that a smooth focussing action would indicate a recent disassembly for relubing is very astute.) Might as well take it apart and put it back right.
“Believe nothing, no matter where you read it or who has said it, not even if I have said it, unless it agrees with your own reason and your own common sense.” – quote
I myself am made entirely of faults, stitched together with good intentions. -quote