I noticed the coin tray was open today and found it didn’t latch when pushed back in. Pulled it completely out and discovered the plastic latch has broken so the hooked end was missing hence the problem.
Fortunately the broken piece was still there sitting in the aperture.
Not going to find one of these easily so took it to pieces, araldited the broken part back on and then plastic welded with a couple of bits of stiff wire to reinforce.
Put it all back together, refitted and hey presto fixed .....hopefully this will now last another 25 years!