Here is a pic I took of the gasket last night, Ive seated it in the top part of the cover, if you look closely you'll see the bottom edge is way off.
Is this what it looked like to those that have had a shrunk gasket?

 

Just thought I'd post an update.
I fitted a new gasket using Permatex Ultra Grey, leak has been fixed :P
The original gasket had shrunk, so couldn't be reused.