I have a set of 4 sash locks on various external doors. They are 30
years old and it's often a struggle to get the key to turn. If I had
to get out in an emergency this could be a problem. They do open in
the end after a certain amount of jiggling. I've oiled them and
checked the lock is correctly lined up with the slot in the door
frame.

I'm faced with a £200 bill to replace them.

Before I am forced to spend the cash is there anything that can be
done to ease them up.