CHeck out the TSB's for coolant leaks in GM vechiles with the 3.1,3.4,3.8 and 5.3. You might also check out the TSB's on oil consuption, piston slap and rod knock. The main offenders are the 3.1,3.4,North Star's,Vortec 5.3 etc... Even the flagship Corvette has been plaged with excessive oil consumption and piston slap. I forgot to add Saturn 4 cylinders to the list as well.
The said part is that prior to GM puting a plastic see (Dupont Nylon 33 or 66) upper intake mainfold on the 3.8 it was a relatively problem free engine!
GM has redesigned the intake gaskets, torque spec., torque sequence, and thread sealant used many times trying to stop the 3.1 and 3.4 from being so leak prone. To date it is still issue. THe design and materials are just flawed and to be significantly redesigned or droped from production all together!
GM has even tried sophisticated decarboning/cleaning tactics to fix oil consuption and slapping noises! To little avail!
To all the GM Nazi's this is not an anti-GM post simply stateing historicaly significant facts. They can be researched at Alldata or any other place that list's TSB's and recalls by manufacture!