I have MY 05 Forester X and I bought it used. I assume that the shocks are are OEM and have not been replaced. I just rolled 60K and was wondering if they may still be good or not...is there a definitive way to tell?
Assume nothing. If you know (or can guess) the dealership(s) that serviced the car, call their service department and ask if the shocks have been replaced. You don't need to know the former owner's name, but you will need the VIN number (last few digits) of the vehicle VIN. I have found Subaru dealerships to be very organized and super helpful.
Another user mentioned the 'push down and release' test. Possibly denting the safety bumper notwithstanding, that test doesn't work so well on newer vehicles. It is worth trying, but even if the vehicle settles in place with only one bounce, the shocks might still be flaky.
Mileage is probably the best test. If the shocks have 100k on them, consider a replacement. For the best handling, a 75k replacement is not out of the question. This is a high-wear component. But, I guess it depends on your budget.
As for the wrenching replacement, I just went through this. An impact wrench is handy but not really essential - we used one to remove the top strut bolt and spin the spring compressor.
To remove the two big bolts at the bottom of the strut, get a 1/2" drive (1/2" drive minimum - 3/4" drive would be better) breaker bar and a 4' cheater. The nuts will come off like butter.
Borrow a spring compressor for a local auto parts store. Jack up and support one end of the vehicle at a time - the whole front or whole rear. Don't try to jack up a single corner only - twists things around too much. For the '05 X, you don't need to undo the brake lines.
Finally, be sure to completely support the front hub (use a jack, milk crate, whatever) before you remove the strut - you've been warned! Two persons can do all 4 corners of the vehicle in 3-4 hours - maybe less.