Re: Oil in exhaust?
I think you can trust your dipstick... Check it with the engine off and wait a couple of minutes for the oil in the galleys and lube system to drain back to the pan.
What you saw was probably soot/unburnt fuel rather than oil (or mud, for that matter - esp if you sailed off and didn't churn up any silt with the prop) If the black is unusual - ie - you've run at 2500rpm without issue previously then something may have changed.. but if it's fairly new-to-you and this is the first time you noticed it that's another thing. You might be overpropped, that can lead to what you describe, or your prop could be dirty/fouled and causing the engine to run at a higher load, either can lead to smoke/soot at higher revs...
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)