Finally got under the MG today to sort out my slowly worsening exhaust blow. I was expecting to see a hole or split in any one of the exhaust components, but no everything seemed fine and intact. The blow seemed to be coming from top of the system, so off with the inspection cover (what a b@stard job that is, but that's another story!).
It turns out that out of the 5 manifold studs, the bottom 2 had disappeared, the top middle 1 could be unscrewed by hand and the 2 top outer ones weren't exactly tight!
Luckily I found 2 bolts that were exactly the right length and with a couple of spring washers managed to fix the problem!
Need to source some proper replacements and manifold gasket to do the job proper!