Those are exhaust flanges and the nice replacements are $150 for the pair so well worth your time to remove and renew. Mine were horrible and rusty after just a few seasons.
Give all the joints of your exhaust a good dousing with your favorite penetrating oil and let it sit overnight.
Remove, clean and polish starting from the mufflers and working forward. Blast or wire brush the flanges and replace the gaskets if they look perished:
http://www.mgcycle.com/index.php?main_page=product_info&cPath=26&products_id=1406Paint your flanges and replace with copious daubings of anti-seize on all hardware.
Put the exhaust together very loosely and make sure everything lines up.
With everything loose you can push and pull things into place before you tighten. Start with the head pipes as this is the critical fit.
The head pipes must be flush to the head to get a good seal. Now work your way back to the mufflers and you are good!