The more I read here the less I think you have an issue. Plugs seem fine (best indicator), no significant loss of oil or water and performs well. I know when I do not drive my '71 Chevy for a while, it blows some nasty black flecks out the exhaust on start up. My theory (and I believe others have eluded to this) is that the condensation in the exhaust is mixing with some of the soft, sooty carbon and that's what causes the black specks..

I think those black specks on your trailer came shortly after start up of the engine.

Take the car for a long drive and get things all warm and toasty. Shut the engine off and then hold a piece of cardboard near the exhaust while a helper restarts. You'll probably not see anything.

Next time it's stone cold and been sitting for day of two, repeat the process and you probably see some of the black specks.

If so - I'd not worry too much as long as oil and temperature remain normal and you do not notice a change in performance.

Enjoy!
Glenn