Your contra is most likely OK some little bit of oil around the compression screw is not a problem usually after a while a lillte soot will build up around the compression screw and it no longer leaks. A couple of mine did this (irvine comes to mind) and it eventally stopped
just a trace now and yes a little gets past the contra in all engines this is normal. Some if us have actually drlled a small hole in the top of the head to relieve any pressure buildup and the chance of ignition of the charge in the space between to top of the contra and the bottom of the head this is not an issue in smalll diesels. martin