I have Shelby block #197 and the Aviad pan too.
Thanks to this site, I am a firm believer in the Motorcraft TA-31 RTV sealant (amazing nasty stuff!) and I always keep a pair of Milodon #40450 pan gaskets hanging on the wall just in case. I have yet to have to use them.
As far as removing an Aviad pan in the car, I seem to remember the Kirkham's posting some advice on that subject a long time ago. Might do another search or give them a call.
All that said, I have minimal problems with rear leak. Knocking on wood!