The northstar is not none to crack blocks. They are famous and notorious for head gasket leaks and head bolts pulling out of the blocks. There is a gm service bulletin on this. I would have another shop check it out to confirm.
File In Section: 06 - Engine/Propulsion System
Bulletin No.: 00-06-01-016
Date: August, 2000
An enhanced thread repair process has been developed for use on General Motors aluminum engine components for the above listed engines. The thread repair kits used for this process represent a significant advancement in aluminum component thread repair, providing consistently repeatable high quality repairs which, when properly performed, will meet or exceed the original specifications. This enhanced thread repair process can, and should, be used to repair aluminum engine components, instead of complete engine replacement, whenever possible. Kent-Moore has distributed these thread repair kits to General Motors dealerships as part of their essential tool packages. The J 43965 Thread Repair Extension Kit has proven to be invaluable in the repair of difficult to access thread repair locations. Listed are the Engine VINs / RPOs and the applicable Kent-Moore essential tool thread repair kits.
Consult the appropriate applicable GM Service Manual or Kent-Moore thread repair kit for complete detailed instructions on the proper use of the above thread repair kits.
For vehicles repaired under warranty, use: