1 Lucky Texan

the cap/o-ring problem is not too bad to inspect for, I just dunno if the Forester's design is similar. I may not know exactly what the issue is here - but can't help wondering a coupla things; suppose the input of fuel is disturbing some debris in the tank that collects on the 'sock' - but temporarily ???? any whooshing of air when the gas cap is loosened/removed? and sense if air is moving in or out? I'd be tempted to try 2-3 tankfuls with Techron (maybe seafoam?) or similar gas treatment, maybe some odd check valve is sticking somewhere???? maybe scan the ECU and see if a code is pending?

pull plugs when it's cold - before any start attempts, see if any are wet with fuel. maybe cylinder wash-down is part of the problem?

manufacturers consider something like a quart in 900-1200-- miles a problem. A qt in 3000-5000 would not meet warranty-levels of concern I don't think. you might try a new PCV valve. You might send a used oil sample to Blackstone. maybe a leaky injector is diluting the oil or ????? but 750, yeh, you could call SOA, explain to a regional rep that you already documented a concern in the past, and now experience a very high level of usage. Maybe you can get another test done but, at this age, who knows what Mother Subie will do??? I'd prepare myself for disappointment.

plug looks good to me - minimal residue. I realize it is xtra work, but axles are L-R exchangeable, then, if the turning noise moves with the axle, that should exonerate the diff right?

if you go down 25, and if you have time for a 'side trip' take 12 out of Walsenberg to Cuchara, then to Trinidad. awesome scenery.

Akro, if you decide to replace the trans, do a search of the forums and internet about seating or retaining the torque converter. If it slides forward, it can cause issues when bolting in the trans. Possible cracked hydraulic pump.

France, might be tricky.

yeah maybe the switch or the 'button' on the pedal? some models have an issue with the button falling out...my brain doesn't recall what generations have that lol

any exhaust system damage? you may need to look at live data from the ECU

Dave mentioned wires, you say the car has been sitting, you should look around for rodent damage I think too.

ABS is very sensitive to system voltage. Some (maybe not all) of the symptoms point to a charging issue and, knowing that the H6 has a special alternator, I can't help wondering if it is failing or, if aftermarket, could be the wrong style. I thik getting a voltmeter on the battery terminals or elswhere and checking/monitoring voltage is a good first step. A fully charged healthy battery will be around 12.6v, charging can range up to over 14.4v, maybe 0.2 - 0.3 more. But the ECU in that car can hold charging current back. are there any aftermarket electronics in the car? CB radio, woofer amps....etc.?

I wouldn't swap 08 with 01s. Tell us what problem you are having.

????? I like the ground cleaning you have planned. Throttle Position Sensor could have a 'dead spot' in its mid-range sweep. though I wouldn't overlook the possibility of more than a single issue given you symptoms. could be battery cable is corroded under the insulation. Possible bad Knock sensor - cheap easy to swap, if bad, often the plastic housing will be cracked. automatic transmission? aftermarket axles can cause vibrations when stopped but in gear, goes away in P or N - seems weird, but it's a legit problem for some folks. I suppose, if the car is missing at idle, you could squirt some ether start or even an unlit stream of propane from a handheld torch into the intake.If it smoothe-out, could be a fueling problem. Have you measured the system voltage?

tell us about the starter replacement. Did the original fail a bench test? Is the new one a parts store rebuilt? Did the replacement ever work?

another longshot - clean or replace the crank position sensor. Sometimes metallic debris collect on it (often from failing bearings - looking at you Toothed Idler).

others can comment, and actually, they have a lot more useful info that I ever will specific to that engine. But, looking at the big picture here; consider this a totally new project. Perhaps converting back to all VW is an option? Or, converting to a Subaru EJ engine?

if you own a smartphone, an inexpensive adapter to read trouble codes can be had for under 50-60 bucks. Vpeak makes some, check amazon. Some apps are free like Piston or torque lite. a P0420 code has cat conv in its definition, but often something like an exhaust leak or vacuum leak or rodent chewed wiring or ??? can be the real cause. Never assume a trouble code points directly to a part - it is a symptom. you might also like to read-up over at www.subaruoutback.org - also great folks

next 2 suggestions are trickier; if a spacer at the top of a strut assembly (under the strut mount) is upside-down, it will drag. It is narrower on one side to rest only against the inner race of the bearing in the mount. Or, mount bearing itself is severely failing? You can take the rubber plug out at the top and spray some lube in the bearing....might make a difference. I suppose a rack issue is also in the mix here, maybe others will have ideas?

replaced the rear wiper arm. Grandson ripped it loose. Not happy with the quality of the replacement. Saving the original to try to come up with some approach to reinstall. maybe some thread locker.....?

are those directional? I only ask because, I have a dim memory of some thread about that, seems that it mattered because of preventing or causing fluid to push past the seals? anyway, they should pop-out with a circlip/spring clip on them.

daveT's suggestion is pretty good I think, get an engine from car-part.com , MLS headgaskets and new timing belt system components.

all 4 new tires? all tires must be the same size/model/brand and near each other in wear. Will the car perform smooth, slow tight circles on dry pavement? no jerking/binding?

even here, I miss it as much in winter as in summer. I drove an '81 Honda Civic wagon for over 10 years with broken a/c (no money to fix during those year) - not fun in August....but I survived.

You might investigate a propane/butane mix. From what I have read, not as dangerous as it 'sounds'.....I mean, you have 10+ gallons of gasoline in the car anyway.

year? any pics?