There's a hell of a lot of people out there with so much cholesterol build up in heart arteries that they could have an attack any time, they just don't know it. They've got 85% blockage and everything seems fine, then one day it's 'adios'.

That blockage in the riser would be a difficult one to address as standard maintenance. I don't think that scheduled maintenance has you taking your exhaust system completely apart every couple of years.