2006 XC90 4.4l – P0430 code

I have been working on this problem for the last 3 weekends. Here is my log to date:

1. Clear code. Add 1 gallon of lacquer thinner to approx 10 gallons of premium gas. Do Italian tune-up for 350 miles. P0430 came back the next day.

2. Install new OEM upstream oxy sensor (as per Mitchell-Pro advice), clear code, repeat Italian tune-up (no lacquer thinner, just premium fuel). P0430 came back.

3. Jack up XC90, put on jack stands, engine running, lay under car, use stethoscope on intermediate pipes: bank 1 nice and quiet, smooth sounding at idle and while revving the engine; bank 2 noisy/puttering, very noticeable.

4. Pull spark plugs (OEM iridium's) and compare: all VG, clean, condition. No tell-tales like excessive carbon or sludge.

5. Do all the crap one must do to drop the engine cradle and remove bank 2 exhaust manifold/cat assembly.

6. Cylinder #8 port appears suspicious : looks like pin holes near the neck on the bottom side and along the weld seam on the top side.

Have look at the photos. What do you guys/gals think?

Update: 03/26/2015 2:32pm: I wire brushed the areas with a dremel and can't see any pins holes.

Last question then: has anyone installed one these aftermarket manifold/cat successfully (no codes afterward)?
http://www.ebay.com/itm/Magnaflow-Di...9e4bd3&vxp=mtr

XC90 - P0430