Ah OK, the exhaust tip that pokes out in the centre of the end cap yes? Not sure what that's made of to be fair but bits rotting away does sound less than ideal. Maybe pop a photo up if you can just to be sure.
It might also be worth checking the joints for blow by regarding the noise issue, exhaust clamps (especially the rear) have been known to rot and fail which allows a tiny leak which eventually burns through the gaskets and causes a much bigger leak.
Replacing with OEM looks like it's all one piece bar the two header pipes off the cylinders. Bit of a job and some new gaskets but nothing too daunting (apart from the price if using a new Suzuki part).
After market appear to come with or without front header pipe depending on brand.
As Sea-Strom says, accessing to replace a rear header pipe is a nightmare but shouldn't be needed here.
