i have recently had a engine rebuild and have covered about 1300 miles since. i have given it a good run today (280 miles),butwhen i was putting it in the garage i noticed some moisture in the tail pipe. on closer inspection it was a black substance quite thin with a slight oily texture to it. is this somthing i should be worried about?

 

Did you ever watch the X Files?

 

you sure it's not soot + condensation ?