Some more questions to keep you on your toes....no nodding off at the back!

  So, when I cracked the cases there was some evil looking gunge that looked like rotted aluminium in the triangular void at the front of the engine.

What is that stuff? How can I prevent it coming back (seal the surface perhaps) and should I be concerned?

On peering inside the crank cases I've noticed this nasty looking burr below the exhaust camshaft on the timing side of the cases.

I'm going to Dremmel it to death but before I do is it just a bad casting or a sign of something more sinister...