RE: DA 100 Break in ???
Check to see it both exhaust outlets have about the same oiliness, if they do it is probably mostly on one side of the plane because of prop wash etc.
If the residue is black it may mean you have a loose exhaust system on one side, aluminum rubbing against aluminum will make a real mess that is hard to remove.
If the exhaust system is tight and it is real black inside only one exhaust outlet look at the piston with the header removed and be sure the piston does not look damaged/scuffed.
Assuming that the residue is only oily but one outlet is noticebly wetter it could be that one cylinder is running richer than the other specially at less than full throttle, if you do lots of part throttle flying, this will probably go away after break-in for the most part and after you switch to synthetic.
Assuming that the engine sounds good and is not running on one cylinder sometimes due to something wrong in the ignition system hopefully you will be able to determine what is happening.