I've got the exhaust system out for driveshaft work. It's been loud for at least 100,000 miles, but shows no signs (externally) of needing replacement. All one piece, welded together, it's a silver color except the short pipes near the front pair of mufflers (they're rusty). I bought the car new so I know it's original. And it weighs a ton--probably 75 pounds.

Questions:

1. could it be full of soot? What does a new system weigh?

2. can I test the flow somehow?

3. should I replace it or just put it back in?

-Thanks.