Should I replace the donut gasket that goes between O2 housing and the downpipe when putting a new 3" downpipe? Also I remember seeing the donut gasket on the O2 housing before and it looks like melted on the O2 housing from the heat, is there way to take it off or you just put the new one over the top of it?

 

No, get rid of it.

 

well i have a brand new one from mitsu if you want, a donut gasket that is.

let me know at allyoucantiff@aol.com, i'll sell it for 10 bucks shipped.

 

I replaced my gasket between the o2 pipe and downpipe when upgrading to a 3" downpipe at 15,000 miles. The original looking perfectly fine, but I replaced it anyway while I was there.