Seal incompatibility is no longer an issue with synthetics, so it's not that. If you are not using Mobil 1 (any grade), Castrol Syntec 0W-30 (only the one that says "made in Germany), Amsoil (except the XL series), or Motul, you are not using a true synthetic oil to begin with.
The cam seals might be leaking. This does happen; just go get it fixed. Should be fine after that. Others have reported the same issue at earlier mileages.