Behold:-

The offending mechanism.


Good job I finally took it to the professionals, even they couldn't loosen all the screws without snapping some.
Yonder gaping orifice ought to be a plain sheet of metal; though, in mitigation, it's only fair to point out ye Wagon is 19 years old, so I don't suppose it's done too badly?

Some of you may recall an ancient price illustration, which terminated in "an itemised invoice" which read as follows, in "Olde money" of course.

"To turning Screw 6 pence.  To knowing which screw to turn, how far and in which direction - 19 shillings & 6 pence.
TOTAL =£1-00s-00d

You could, of course, say 5P & 95P = £1.00
:¬)