When I removed the 2 fixings that hold the rear of the hood and hardtop I was surprised to see that there was no gasket or seal between it and the body.
An old car inner tube I have had for years comes in handy again which makes a great source in the making of thin rubber gaskets / seals.
A previous owner had not used the correct cup washers to fit them which was probably why they were always a bit loose.
Trouble is fitting them is a bit fiddly. Easiest way I found was to use some blue tac to hold the screw and new cup washers onto the screwdriver to avoid losing it.
MGB tips mods and maintenance 