Valve Guides?

[bosalls5]

I'm a new owner (2nd) of a 99 C2 Carrera, 70,000 miles. Engine was replaced under warranty in 2001 (55,000 miles +/-). Right exhaust tip is showing more black residue compared to the other side. Car performs very well , accelerates like it should, etc. Seeing the residue my 1st thought was rings or valve guides in the near future? Or is this normal occurrence? What do you think?

[Bill Verburg]

Worry when there is smoke pouring out of the exhausts