ANOTHER major repair - rear ball joint need replacing

It shouldn't be necessary to mention this, but go to a Indy subaru specialist, not the dealer.

That being said, it is surprising to need to have to have a ball joint replaced at 76k miles, and I understand your anger. Concerning the HG, unfortunately all the 00-09 subarus all have to have the HG's replaced at some point. It is an indictment of subaru that they let this problem fester so long. IMO, they should solved it by 05 at the very latest.

lubrication

Ball joints fail because of lack of lubrication. You might have cut the seal and the grease came out or during greasing the grease gun over filled it. Visually inspect your joint periodically.

Update

Thank you for the feedback, I had heard the headgaskets were a problem. Annoyed about the ball joints though, tell me more....does there need to be a physical impact for the cracking or does it happen from neglecting lubrication? I had read somewhere that it needed to be a part of the maintenance alongside the oil changes. I hate to think this, but from other things I have heard recently, I wonder if some of the maintenance is "forgotten" with the intention being a part fail that would bring me back in for another repair....

sorry, just re-read your post. Overfilling would prevent the closing and ultimately cause it to "dry out"?