That has happened to me some time ago, I was looking for a second body, and ordered one second-hand R-D1 from a shop in London (Aperture). From day one, these black frames were happening, I tried all batteries, new ones, didn't change. So I quickly sent it back to them and got a refund. For your info, they sold the R-D1 to another person later, without doing any prior service - that tells how serious some can be -.
Fortunately my first R-D1 body never had this problem so I kept it.
From this experience and what I could have read elsewhere, it sounds more the shutter mechanism needing a replacement and it would be worth sending it to Epson Japan and have the camera back "as new". Not cheap, but they do a great job, in my view and experience, much better quality than Leica service and way cheaper.