I have the original type of rocker cover which i had spent a lot of time stripping and repainting it a while ago and decided it was now a good time to fit.
When I fitted it I noticed that although the two nuts at each end were getting tight and clamping the gasket at the ends the central section of the gasket was obviously quite loose.
I guess after years of use and over tightening the cover has distorted taking on a “banana” shape!
So I found a flat surface which happened to be my garage floor and with a hammer and a piece of wood hammered the flange back to shape. To check it I placed the cover on the bench over a torch to see how much light I could see under the central flange area. The gap soon reduced from nearly 2mm to almost nothing so refitted the cover …….. and so far so good.
MGB tips mods and maintenance 