nvu

With the belt off, spin them. If they freewheel and sound like roller skates there's no grease left inside. The cogged idler is under the most stress and likely the first to fail.

Here's a video for the impreza, different car, same engine. The plugs are a pain to get to, have a look and decide for yourself.

https://parts.subaru.com/a/Subaru_2009_Legacy-25L-4AT-4WD-Limited/_54102_6024341/EXHAUST-EXHAUST-COVER-06MY-/B13-440-10.html There's a gasket 3" away from the rear o2 sensor. 44184. It doesn't look like the older donut style that tends to leak though. I tried https://www.google.com/search?q=subaru+2009+legacy+p0420, only thing that sounds plausible is cleaning the maf.

no lean code means the front o2 sensor is happy with the air coming out the engine. p420 is when that air goes through the cat and hits the rear o2 sensor. the engine is fine, the ecu is not happy with the air coming out the cat. exhaust gaskets, bad o2, bad cat. nothing to do with intakes

If it's not hard metal clacking chances are it might be a failing tensioner. Take the covers off again and do the prybar trick to test.

you've already removed the oil pan and pickup tube? it should lie flat, normal upright position on the table. if there's not enough leverage, put it on a carpet floor and step on it as you unbolt.

Was there much rust when you did the balljoints? If those came out easy the bearings would come out easy also. Get the press kit, unhook the ball joint and you'd have enough room to do it on car. I like to also unhook the tie rod to get even more access. Make sure you find and remove the snapring.

$100 sounds too steep. Do you have autostores that rent tools nearby? A bearing installer kit is all you need, probably under $100 to buy one outright. https://www.google.com/search?q=bearing+installer+kit There's also a snapring hidden under all that grease, be sure to remove it before pressing.

if you want to check for wheel bearings, jack up so both front wheels are in the air. spin one wheel by hand while holding onto the strut coil. you'll feel some grittiness on the one with bad bearings.

there's one sense wire and one ground wire. splice in the old connector. ground wire has continuity thru the bolt, sense is the other one. sometimes there,s only one wire inside, that's the sense wire and it grounds onto the bolt.

Likely this. There's a tiny indent on top of oil pump casing. Line it up there, it be near the trailing edge of the crank sensor

assorted o-ring pack from autostore works fine

forgot about that one, good catch!

Maybe you had a bent pan. Subaru oil pans are fairly soft. You can get the lip surface flat again by placing on concrete face down and tapping around it with a scrap piece of wood and hammer. Most times it's the holes on the pan that gets dimpled, look closely at them, flatten those out and it should seal with minimal rtv again. Tighten to full specs, overtightening will just dimple them again. If the engine is out and on a stand it's even easier. Flip it upside-down, place pan on it, and tap the lip flat again. The pan is that soft. Similar idea in this video, I use scrap wood instead of a metal chisel.

Ultra grey works best with flat surfaces. Full torque if both mating surfaces are machined. Case halves, oil pump to block, cam carriers, etc... The finger tight, allow set time, then full tight is for imperfect surfaces like stamped oil pans and covers. I don't do it, just torque it down and let it set.

Oh, I read that wrong. I haven't seen a spring clipped stub axle yet, all the ones I've dealt with has snap ring style circlips. And they rarely break as others have said. Maybe just pull out the axle and wiggle the thing, guessing it should be obvious if it's shot.

Check if there's a rollpin to punch out. If so it's a female axle and stubs on trans like pictured above, no oil spill.

i've had good results welding plastic bits back together with a plastic soldering iron. picked up one at harbor freight, it has a triangle tip and seems to lower heat point than standard soldering irons. I've fixed door cards, headlight tabs, window switch panels, etc... it took some time fiddling with techniques until you get to feel on how to melt plastic just enough to weld and not too much that it becomes brittle. if you get the hfreight kit, the black strips they supply is hot glue and not plastic. you'll have to get a separate plastic rod welding pack or just use whatever spare plastic bits you have as welding material. i've found the black abs plastic from old dell lcd monitor covers to be really good for this.

looks like you already have the bracket, oops it's missing a bottom bracket for the compressor. for the tensioner, you could skip it all together and get a stretch belt directly from the crank to the compressor. here's a diagram, it's 73611 https://parts.subaru.com/a/Subaru_1998_Impreza-22L-MT-4WD-Outback-Wagon/_54104_6022881/COMPRESSOR/G10-732-02.html

Definitely pull clutch hydraulic then. If that's the trans, it will cross reference with 02-05 usdm wrx. You might wanna double check the new clutch and clutch cover to see if they match. If not, the exedy ksb-03 kit is oem replacement for that trans.

Looks like you have a pull style clutch. It's the same bearing for all 5mt pull style transmissions. Here's the part, use the crossreference to find it elsewhere, should be no more than $50 last time I got one. https://parts.subaru.com/p/Subaru_2002_Impreza-205-5MT-4WD-WRX-Wagon/BEARING-CLUTCH-RELEASE/49239161/30502AA130.html

sounds like the clutch doesn't fully disengage when cold. with the engine off, is it easier to shift into gear? if so, likely nothing wrong with the transmission. bleed the lines and check the pedal adjustment. if it's a push clutch, sometimes the fork cracks and bends causing these issues.

water pump shaft seal is bad

unplug the switch, see if it goes away. if not, look for the tail/illumination relay, pull that out. if that doesn't turn it off, something aftermarket or is wired different from factory. This is from a 98 impreza, similar setup as legacy

it just sits in there spring loaded. the tension is enough to keep it from backing out. these aren't high torque bolts so that should be good enough