[William Wiles]

Why not diagnose the problem instead of throwing parts at it. Did you have the Po141 code when you had the P0420? A bad O2 sensor can cause the p0420. P0141 is an O2 heater open code. Use a voltmeter or ohmmeter to check out the O2 sensor in the converter. If it started when you replaced the old one or converter chances are the wiring got screwed up. Use a voltmeter or ammeter to check it out.

 

[William Wiles]

Google 'oil drain plug repair'. There are repair kits to repair it.

 

[William Wiles]

I put a Fumoto valve on my 04. Eliminates all the pressure on the threads.
As for the po420 have someone analyze it with a good scanner.