Long story short, read the title. I'm worried that this might be yet another damned expensive repair. Some background below. Hoping to get some advice from seasoned Subaru owners.
Me: I'm a poor grad student, at least one year from graduation. Must have a car. If this one dies I've gotta go find another. Hoping to keep this one, since I just spent a bunch of time and money replacing clutch and doing front end work.
My car: 1999 Legacy Outback, 2.5L DOHC, think that means it's an EJ25D motor. I bought it in 2011 at 198,xxx miles. Now at 227,800.
Previous owner told me he replaced head gasket and some other major work---really wish I'd written it all down.
I replaced ignition coil, plugs and wires (2 summers ago). Wires look OK visually at the moment.
Just a few weeks ago, I did my first major project---replaced clutch, rear main seal, oil separator pan. I removed entire exhaust system in order to do the repair. Dropped transmission, rather than pulling engine.
The problem: My exhaust started getting loud in the last week or two. Suspected exhaust leak. Also, the check engine light came on yesterday, indicating P0301 & P0303 (cylinders 1 & 3 misfire).
Took a look under the car this morning and realized a welded hanger hook had broken off and left a hole behind. I picked up some fiberglass exhaust repair tape and patched the hole. (Perhaps not relevant to the misfires, but including it just in case). I took a 20-minute cruise per the instructions on the exhaust repair tape. On my drive, CEL flashed & came on again. Codes were P0301 and P0303 again, plus 2 more codes: "P0301 P" and "P0303 P". (What's that extra "P" mean?)
I did some reading on these forums. Since the 2 misfires happened simultaneously, I suspect it's not the plugs or wires. Also, I've seen some talk about timing belts related to this kind of problem. I do not know when my timing belt was last replaced, so it was at least 30k miles ago (i.e. previous owner).
Finally, this thread indicated that it could be "burned valves." I tried the "dollar bill trick" someone recommended on that post. Seems like the behavior of the bill depends on where & how I'm holding it... but I'm afraid I "failed" the test. :-( I posted a video on Youtube of the dollar bill test. (below).
Based on these symptoms, have I definitely got burned valves? Could the "dollar bill" behavior be caused be a less severe problem? What should I do next...? Get a mechanic to diagnose further? Can I do this repair on my own? Given the age of the car, and the time & $$$ expense of a repair, what would you do in my shoes? Thanks for any advice. Cheers.