The first post just says you have checked the pipes mate. Doesnt explain how? Just looking does not give everything away, although you should be able to spot the obvious.

Also yes most are crackd after 20+years of abuse and higher than std boost levels. It will of course make a difference depending on where the crack/s are and how big etc. It would be best to get one that isnt cracked but after abuse it will crack anyway, so its a no win situation. I norm use volvo .48 or saabs, as most of these have not been molested by the likes of us and run pretty safe levels of boost and heat etc.