Does the car have to be overheating to destroy the bearings? In other words, if the intake manifold has a crack in it but the vehicle isn't overheating, will the bearings still be thrashed?

No. You'd have to have a total coolant loss and overheat.

They have to use the plastic for some reason, they just wouln't change from all. to plastic for the heck of it. Maybe that'* why the Sereis 2 have more HP, they got a better intake. I don't know really im just making this up.

Series 2 has the plastic intake, too. Hector may have a solution for this soon.

The plastic intake was made to save money and weight, and the design was also to increase performance. GM could have made an aluminum intake with the same design that would have given the same performance.

As for what damages the engine when these intakes fail, it is the hydro-lock that occurs when the coolent is ingested into the engine. Coolent, being two dense to flow through an engine at 2000 RPM, will lock up the engine, causing bent/broken rods and valves, and possibly spinning the bearings in the process. The other scinario--as Will pointed out--is that the engine may seep all the coolent out over time, not producing a hydrolock situation, but causing the engine to overheat, which in turn renders the oil ineffective, thus allowing your engine to score and/or spin the bearings. Neither situation is favorable.

These engines are great engines. The lack of maintanence of one poorly designed part can be a fatal mistake to an otherwise near-perfect engine. GM will not conceed to replacing or redesigning this part as it would open them up to lawsuit. It will not be a recall issue because it has nothing to do with safety. The only way to change this is to link fatalities to this problem--which, given the safety features of the H-bodies, is very unlikely. Hectors breakthrough (if he developes one) would have the potential to put ADTR on the map with the right price and marketing.

I wouldn't worry too much about hydrolock, but keep it in the back of your mind. You would have to have a HORRENDOUS leak into the intake to cause that. If you really wanna know if you're burning coolant, pick up the gasket kit for the upper intake, and remove it. The upper isn't that hard to do. If you have a coolant leak into the lower intake from the seal of the upper, you'll have one or two clean intake runners from the benefits of 'water injection'. Jseabert had one really clean one, and 5 carboned up ones. It was pretty obvious. He was loosing about an inch of water in his reservior after a 30 minute drive.