The trusty 4 1/2 inch grinder is a great tool for this kind of exhaust work. Something like this: http://www.homedepot.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10051&langId=-1&catalogId=10053&productId=100006889&N=10000003+90401+527282

That'll make quick work of rusty nuts and such. Just have to be careful handling the hardware because the grinder puts a lot of heat into things.

If you ever plan on taking it apart again, I suggest getting stainless bolts and nuts at your local hardware store. They don't cost much more and *should* make the job easier next time.

Or you could get an 850 and it's likely you'll never have to do any exhaust work...

--Will
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850 / Mini