Look for cracks at the beginning of the header pipes where they bolt into the engine. If not cracks then possibly the two bolts need tightening. There are stoppers on the nuts but they have been known to fail. On mine the stud itself broke off and the rest of the bolt and nut were nowhere to be found.

There are a lot of stresses in this area as the engine moves a great deal in relation to the pipes. I've also had a header crack in that area due to excessive movement. As the pipes themselves can glow cherry red any stress at the wrong time can rip them like wet cardboard!

Also look for oil spray or the tell tale smell. The valve covers may need tightening and that can stink.

What's your mileage? Who cares. Is it practical? See #1. What happens when it rains? You get wet.