catalytic converter

Hello, I'm relatively new here (sorry if this post is in the wrong place or anything!), but figured I would ask since Googling hasn't gotten me anywhere. So long story short, I had error codes for O2 Sensor in Bank 1 which since has been replaced, however at the same time I had an error code...

I have check engine light. Autozone drew code #P0420 ( possible catalytic converter defective). After-market part cost $300. Scott Kilmer suggested pouring a gallon of pure lacquer thinner into the half-full gas tank and drive 150 miles and it will clean the cat converter and erase check...

Yesterday I replaced several light bulbs in the gauges of my '03 Elantra. I was surprised to find out that there are so many bulbs there. Basically there are three different sizes of bulbs: large, medium and tiny. I had ordered all the bulbs necessary to change from a local Hyundai dealer...

Help!! I need to replace the 2nd cat, but can't seem to find the right part online. The existing cat has a 90 degree turn up before it meets the flange of the downpipe. All parts I find don't have this 90 degree turn. I actually bought the part from autopartswarehouse.com (WHAT A MISTAKE)...