I was using my fairly elderly low-end Ferm rotary hammer to do some
heavy-duty chiseling and the tool fell out. When I tried to replace it, I
discovered that the rubber sleeve would no longer pull back.

Removing the sleeve and the small additional grommet-type thing that sits in
front of it didn't leave me any wiser: the shaft of the chuck still moves in
and out, but even at its extreme inward position the tool doesn't lock.

Looking into the chuck I can see the lengthways raised strips which guide
the tool in, but no visible locking mechanism - which I've discovered from
an online search should be a ball bearing.

Does this mean that the entire chuck has to be replaced? Another quick
search hasn't thrown up a source, but even if it had I suspect that it might
be almost as expensive, and a great deal easier, simply to replace the whole
thing. Am I right? Comparable budget models seem to be around for £50 or
so.

Many thanks.