The exhaust pipe on a 6490 at work has rotted through at the elbow in the black box by the isolator switch and the silencer box has blown through towards the top making a complete system necessary , tractor is a 2008 model and has completed circa 6000hrs, local sub dealer Keith Davies Agricultural has quoted the sum of around £ 1000.00 ( parts only labour extra) to replace the whole system.
This equates to 16.6 pence /hour just for the upkeep of the exhaust system or to put it another way...
Massey Ferguson parts prices