Caboobaroo

Pull the driver side timing belt cover and peek in. You should be able to tell but I'm almost 100% that it should be the newer tensioner.

Yes, the front bushing has to be changed out. The STI runs a 61mm long bushing where everythin else runs a 55mm bushing.

It's a clean little car. I work only a couple blocks from them and have done a few repairs for them. They have had it for a couple years at least.

A few issues that haven't been mentioned. Being a 2001, it's a first year of that engine and transmission combination. Unfortunately the 2001 have issues with the transmissions which was remedied for 2002. You might be able to swap in a 02-04 LL Bean transmission but I feel like there was a difference in TCU. Second issue. The EZ30D have problems with the Throttle Position Sensor and potentially the electrical harness going to it. The symptoms are slight chugging under load, a flat spot in the RPM range, and general sluggishness up hill without changing of the throttle.

Did you replace the inline filter that goes to the monitoring portion of the EGR on the passenger side strut tower?

With this era, I will always recommend doing the ignition wires with the plugs. I have seen many issues with reusing them and have also had issues with them new from Subaru. I only run NGK ignition wires on this era with almost no comebacks. When you clear the engine memory, there is a possibility it will not relearn the idle (drive by wire throttle). If the idle is low and feels doggy off idle, remove the torque box and clean the throttle plate and body really well.

Sounds like a case of a blown head gasket. A faulty thermostat won't allow coolant to circulate but won't push coolant out of the overflow bottle.

Like I tell people at work. Start by running a good quality top tier gas, either plus or premium. Next step is to check O2 readings and replace the front sensor IF everything else is square. IE no vacuum leaks, spark plugs are good quality and within gap spec and no exhaust leaks. If that still doesn't fix it, then probably time for a new catalytic converter. You can do the anti fouler trick but it's more of a bandaid then anything.

If the axle has been replaced with a subpar part such as a "new aftermarket" or bad remand, it can have excess slop in the joints. This causes vibration sitting idle in Drive because of the joint play. It doesn't do any damage if it's driven like that but it's more of an annoyance and can eventually cause vibration while driving.

Yes. It's physically larger then the EA82 bushing.

Gary, the FWD Impreza runs a smaller rotor then the XT6. I found out the hard way once. Maybe look into an AWD Impreza caliper bracket?

So they're going to build you custom coil overs that mount to a Legacy knuckle? You do realize that if that's what they're doing, you can buy some for a 2000-2004 Legacy fitment. You will need to drill 3 new holes in the strut tower but they bolt to the Legacy knuckles. The rear, being a coil over shock, is similar to the same era of Legacy (00-04). The top hats need to be played with with parts from the original suspension to make them bolt in. It's been done before, with Tein, BC, Cusco and more. Don't let them con you into selling "custom" coil overs for more then the off the shelf ones.

If the boot on the axle has been open for awhile, it can cause the joint to stick, which creates a vibration like you're describing, especially a cheap aftermarket axle. Including the wheel bearing, that's where I would start.

I believe the combination for the front XT6/EJ knuckle is a first gen NONTURBO Legacy single piston caliper bracket and the XT6 caliper. The turbo Legacy runs a twin piston caliper which is physically bigger then the single piston on the L/LS/LSI.

I've seen the head gaskets fail like this and can tell they've never been done. I see it mostly on the 2006-2009 era cars, usually Legacy and Outbacks.