If it's anything like other vehicles I've had, the symptoms won't be apparent if it hasn't sat for awhile. I had a Toyota 22RE that ran fine except when it sat overnight, then it would be hard to start, blow white smoke, etc. I limped it for a while, then finally had to change the headgasket when it started overheating.
Are the Subaru headgaskets similar in that they give you warning? We won't be depending on this as a daily driver, we both work mainly from home, so it's not a big deal to have to deal with changing the headgasket. I just don't want it to go bad when we're 4 hours from home on a roadtrip.
Was the original headgasket design bad? If so, does that mean that once it's been fixed it's then reliable from then on?