The sliding door rattles at the top.  I have several times tightened it
by slacking off the nut under the nylon block, having my wife push in at
the top, holding the block against the track with a screwdriver, and
retightening the nut.  For a day or two it stops rattling  then loosens
up again.  I think the problem is that the block is worn around the
steel shaft.  Suggestions please.

TIA    Earl