Any common 9A1 engine issues?
 

A friend of a friends 2009 997 has developed a knocking/ticking sound from a cylinder and the sparkplugs on 2 cylinders was pretty black (haven't seen it myself) compred to the others.
The sound hasn't gone away with an oil change to a thicker 5w50 oil.

I goggled but found very little, maybe that the DFI engines could have valve guide wear issues?
Apparently its common in other DFI engines (Audi and Mini) with carbon buildup on the backside of the intake valves.

In addition to seizing pistons on #5 and#6, they like to break valve springs, break lifters, and drop valve seats.

I haven't heard anyone else mention those issues, just the dirty intake valve. You sure you are talking about the MA1 direct fuel injection flat six with no intermediate shaft?

Yes, also bad fuel pumps.