After my experience with Coopers I wouldn't believe a word they said. Total incompetence is all I can say about their service! I had a perfectly serviceable Td5, albeit with a blown head gasket, and somehow ALL 5 injectors (yes you read right) mysteriously stopped working while it was in their hands. They have no idea what happened "it just happens sometimes" however after exhaustive research it only seems to happen at Coopers. I wouldn't take my vehicle back to Coopers if they were the last place on earth. Needless to say I had to foot the bill for 5 reconditioned injectors.
As for them trying to tell you that this mod would cause your manifold to crack well that seems to me that what they are really saying is, if you solve this problem we won't be able to charge you to replace your studs ever again!
I agree 100% with Phil, cast manifolds are easily repaired and would be done so much cheaper than paying Coopers to replace your studs every now and again! This mod would not effect the life of your manifold if done correctly.

