Not many replies to your cunundrum Liz!!
I reckon the only thing that could jam a simple mechanism like this would be a broken lever spring. A lot of vibrational bashing might dislodge it. Use a magnifying glass and torch (flashlight) to look as far inside as possible to see any obstruction.
Or, you can file the peined-over ‘rivets’ with a small sharp file and remove the cap - they are easy re-rivet.
You could take the whole drawer in to a locksmith and let them do it.
Richard
