I have a 99 Accord EX and the cat converter went out at 78K miles which Honda replaced in warranty. Now the car has 158K miles and the Check engine light is on and off for weeks at a time. I had the auto parts store check the code and they say it's the cat. Honda charged me a lot of money to verify that but they want tons of money to replace it.

I know a retired Honda mechanic who may agree to do the dirty work and wonder if there is a good aftermarket replacement of should I get a OEM cat to do the job?