Catalytic converter
 

I have had the right side replaced at the cost of $1,500; now the left side is sounding pretty bad - had it patched but still not great. Should I use a factory replacement part or change to a new muffler and assembly?

What year is your Boxster?

Where exactly was it patched?

What does it sound like when it was not patched?

I'm inclined to think if you had the right replaced with an OEM one, then you should also have the left, unless you are willing to replace both with an aftermarket one.