Background Info:

07 WRX
Just under 120K Miles
"Stock" engine (I personally haven't done anything to the engine but it was modified by prior owner and placed back to "stock")

P 0303
P 0304
P 2016

I originally purchased my WRX when I came home from Afghanistan. Subaru Ontario, CA sold it to me "stock." Of course that wasn't the case after I had to drive the car cross country for training. Left it in San Antonio for over a month to repair. At the time compression was lost on the 3rd cyclinder and so they replaced intake and exhaust valves. Six months after this I start to get knocking in the engine take it back in and they decide to replace the short block.

Now my warranty is out because I drove cross country multiple times in the last few years. I had the TGV replaced earlier last year and it was causing the P 2016 CEL. Of course, now that "work" is now out of warranty too.

So I figured I could handle the misfiring codes by changing out the spark plugs and swapping the coils to find out which one needed to be replaced. So after completing that I still am getting the misfiring code for the 4th cyclinder. I did my own dry compression tests and came out with 95/100/95/100. I decide to take it to a Subaru dealership to be diagnosised. Mechanic is saying it's the exhaust valve on the 3rd cyclinder (compression of 75 says the rep) and intake valve on the 1st cyclinder (also 75 on the compression test)...completely different from the 4th cyclinder misfiring code I was getting.

Dealership service rep is saying to remove the heads and replace the valves, it's gonna cost me like $3k in labor alone. I've spent $300+ on the diagnosis already.

I've done maintanence work on all my cars but I have not torn open an engine before. How much of a tasking will this be? I've tried looking for some how-tos but I haven't much luck. I don't mind paying for Subaru's TIS if I can get through this.

I know this is super long but if someone could point me in some sort of direction that would be great. I don't like the dealership doing on the work without me being there side by side to complete it.