Recently my Catalytic converter melted, and after a lot of great advice, I took it off and gutted the cat. My 1987 Vanagon Wolfy runs fine now, but was wondering why the cat failed in the first place? The research I have done so far indicates that my OXS may be bad, what do you think? I do not want to kill my engine, it will go south on it's own soon enough (head gaskets). 

I do not have any hesitation, bucking, or back firing. My headers are cracked in places which allows exhaust to leak. I am planning on replacing the exhaust system some day, but probably later than sooner.

Any advice would be appreciated.

Thanks,

Andy