Got into the unit to find a little accumulated crud!!
You can see the corroded & burnt tabs at 12, 4 & 8 o'clock.
So I made up an earth strap to connect to the endcap..
drilled & tapped the endcap for a 4BA screw...
which was cut flush on the outside, this will be hidden from view when fitted anyway.
Another part to add to the sorted pile!!