GeneralDisorder

No the intake sucks oil through the PCV valve. GD

I have witnessed the expected consequences of an AutoZone PCV valve burning though all 5 quarts of oil on an EJ25. This took approximately 300 miles. GD

Combustion chamber on the SOHC 2.0 heads is considerably smaller with smaller valves. The fire ring on the 2.0 gasket probably wouldn't be a good idea on the 2.5 heads. Might be able to use the 2.5 gasket if there is enough cylinder wall..... would produce an odd combustion chamber shape and lower compression..... if you are already buying dirt cheap EJ20 engines for your project I would wager that replacing the engine entirely would be easier and possibly about the same price/work as buying 2.5 heads and trying to cobble something together. But yes I tried to source some valves for a guy that bent up the valves on his JDM 2.0. Not available in the US. Found some on UK and AUS ebay.... GD

There is no performance benefit to doing this. You're just unnecessarily polluting the air you breathe. GD

Double and triple check your work once you get it on. If you bend the valves on one of those JDM 2.0 engines you are $crewed. You can't buy them in the US. GD

Front main seal. It's like a 5 minute job. But beware. These are not easy vehicles to get parts for. GD

Plastic manifolds have not been a weak point. And they don't heat up your intake charge. GD

There are plenty out there. Just not worth enough for anyone to bother listing them. GD

These are pretty good for cheap: https://www.amazon.com/Creader-Automotive-Scanners-Functions-Diagnostic/dp/B06ZYTDKP3/ref=mp_s_a_1_3?keywords=launch+creader&qid=1554008940&s=gateway&sr=8-3 GD

Generic OBD-II live data from any capable scan tool is generally sufficient. There really isn't much except very spotty unverified SSM support through EVOScan from 95 to 2005. For ~2005+ there is RomRaider which generally can be setup for most applications with some effort. But you really don't need much more than the generic live data. Much more important is being able to interpret the data. Knowing what is normal and how changes in sensor data interact with the fuel system. It's all well and good to see a MAF sensor grams per second or a MAP sensor psi / inches of mercury but if you don't know what is normal in general AND what is normal for that engine family - it's just a bunch of useless numbers. Surprisingly small changes in the data from these sensors will wreak havoc with fuel trims, and driveability. And even that's not enough. It is not enough to know what is normal watching some live data. You have to know under what conditions the sensors are important. You really need a working knowledge of the fuel system feedback loop and how this data is used and what sensors are important under what conditions. By the time you figure it out - you can pretty much design, build, and tune your own fuel injection system. The knowledge and experience is hard won. GD

They didn't fix the coolant leaks till 2002. 99 to 01 models leak coolant and oil. Replace the head gaskets. GD

The 4 speeds are known to have shift fork and syncro problems with 3rd gear. Subaru issued service bulletins and repair kits with updated fork part numbers, etc for this condition. None of which can now be purchased. It isn't a clutch issue (which would show up in all gears, but especially first and reverse) so don't waste your money. GD

Get the dealer ones while you still can. Even at $5 that is a bargain for quality parts. GD

4 speeds are garbage (this you know), and they can't really be "rebuilt" anymore as the parts are no longer available to do so. Put in a 5 speed. If you can even find one of those. Better luck looking though. GD

That's classic clutch hydraulics problem. GD

Burnt exhaust valve. 100%. You won't find a thing under the valve cover so unless you plan on pulling the head don't even bother. Is the engine original? If so it has hydraulic buckets/lash adjusters. They can burn valves though. GD

2WD fronts seem to be around still. Probably not manufacturing them but still sitting in warehouses. Don't see any rears and the 4WD fronts are long gone. GD

How did you determine it isn't working? The auto's are 90% FWD till the TCU sees a difference in the two speed sensors. Scope the signal to the duty-c solenoid. GD

They are no longer available. KYB isn't making them anymore. GD

Neutral safety IS the inhibitor switch (Subaru's terminology) . They are no longer available from Subaru. GD

Rocking the car moves the transmission which is probably causing slight motion of the shifter cable which actuates the inhibitor switch on the side of the transmission. Sounds like you should start by adjusting the switch/cable for the proper park position engagement. The switch assembly is NLA from Subaru so if you must replace it, a used one will need to be sourced. GD

I agree that misfire is most likely. But I just had a 97 in the shop that surged and sputtered due to mostly a dirty MAF. It was pulling 10% fuel before cleaning and adding 0.8% after. GD

Yeah could be a fluid issue too. Or the hydraulics pumping up after a period of use and warm up. I've definitely seen both. Best to use the Subaru HPGO or Motul Gear 300. Both shift well at low temps. GD

The POR15 degreaser works well. https://www.por15.com/POR-15-Cleaner-Degreaser One thing about plumbing the hot water heater to your pressure washer.... most if not all consumer grade pressure washer pumps are not rated for hot water and it will destroy them. Not immediately but it doesn't take terribly long. You can get pumps that are rated for it after you kill the first one but they aren't cheap. GD

Check live data for fuel trims and MAF sensor output. Should be around 3 grams/sec at idle. Fuel trims should be +/- 5% or less. Dirty MAF, dirty intake filter, or sometimes a loose airbox can cause similar symptoms. If you hadn't already done a tune up that would be the likely culprit. Change the fuel filter on principle. GD