A few R3s and S3s (Speed Triple) have had problems with leaking oil from the head gasket. The D675 (Daytona 675) also tends to have this problem with the thinner "race kit" gaskets.
The stock gasket is MLS (multi-layered steel) and requires a very smooth and flat finish on the head and block surfaces.
If a replacement gasket does not fix the issue, you can use copper gasket spray. Coat the gasket on both sides with 3 light coatings - wait 15-20 minutes between coatings. Then let dry overnight.
I do this on regularly on MLS gaskets I reuse a second time.