Did it shows these signs before you picked it up? Not sure of cost, but the SGP's long block or even short block package seems like a good deal for you, seeing that there not to far away from you, say if a problem should occur. Got any pictures of your new Z? Not surprising the number 5 and 6 cylinders readings where so low. It's very hot out there in TX and adding 150k miles on a poorly design motor for cooling the internals off along with poorly designed venting exits only makes what you found out to be true. So the idea of clearing out the water passage ways back by the number 5 and 6 cylinder might be something to look into this time. Upgrading the cooling system is an easy way to go as well for a motor that as oil and water cooled turbo's as well.
