Makita 8391D drill - motor turns but chuck doesn't

[honestworker]

Hi
I have a Makita 8391D cordless drill. I was using it with a hole-saw on an old worktop when the chuck stopped turning, even though the motor was running OK. I can see that the shaft or spindle that connects to the chuck isn't turning. Does anyone know what part is faulty within the drill. Is the cost of replacement parts reasonable or prohibitive? (NB I did once try to repair a B&D corded drill (variable speed switch fault) and struggled to put it back together. I doubt whether I have the skills to do this myself.)
All assistance welcome. Thank you.

 

[big-all]

jumped out off gear /between gears??

is it making any unusual noises [clutch turned to 1??]

is there any feel off trying to work or just noise off a reving motor without any load