Colin,
This would be easy to fix, if you are willing to open the insert, take good notice of how things are put together, and how something is not where it is supposed to be.
These inserts (the problem certainly is with the insert) are rather simple contraptions, and you do not really need a repair manual.
You can get at the innards by removing the screws on the spool holder arms. There is a spring holding this thing down, and it's not always necessary to disengage this spring to do what needs to be done.
Beneath is a long axle, on which is the part that locks behind the "pinnacle" you see inside the shell.
This axle has a bend metal spring where it connects to the key, and i guess this, or the axle itself, will have dislocated.
The other bits in there are are sprung bits that push against the film on both spools, responsible for the red signal in the lock key window, and keeping the film on the take up spool tight.
And, of course, the pressure plate and pressure plate cl& come loose when you remove the spool holder arms. There is a H-formed spring below the plate, easy to see how it should go back. The same goes for the plate cl&: not hard to figure out how it should connect to the other bits.
But if you don't feel like running the risk of having parts fall out and not knowing how to put them together again, perhaps it would be best to let someone else look at it.
