Firstly thanks to all who've responded but I guess I'm going to answer my own question after experiencing it first hand.
I ventured down to the infamous U-Pull-it yard this morning and ended up pulling 5 LH Exhaust manifolds off only to find every single one is .............................. you guessed it...........cracked between 3 and 5. Some more severely than others but it's a real PITA having to do it 6 times all up to find one that hasn't.
I'm wondering how long it's going to be before the welding of these manifolds becomes a standard practice as you can't use the later VY manifolds on a VS due to the EGR pipe being fitted into the later units. I guess they can always be plugged but welding should eliminate the issue pretty much for life. Welding of cast iron isn't a back yard operation and as such most people will have to pay for that to be done correctly.
Anyway I guess this topic has now been well documented for all future questions.