When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
My UPR came with a similar piece and it went inside the drivers side mid pipe where it bolts to the exhaust manifold
Exactly....Mac had a huge problem with the Prochamber not sealing up to the manifold so they started including a metal sleeve, which solved the problem. You might also look into replacing the passenger side exhaust manifold gasket also...check out this write up and you'll be good to go.