Report "The problem with my 3981 relates to the chuck locking button. It has become increasingly difficult (over the past 6 months) to hold in 'the locking button' whilst using the chuck spanner to undo the chuck. The action of using the spanner forces the button outwards-- and I do not have the force to resist this pressure. This means (of course) that I can't undo the chuck. Any ideas what it is that has worn, and how I can get it repaired. please"