I doubt if having run a bit of diesel hurt your motor. I did the same with my 97 BMW R1100RT when the tank truck delivering a load of premium and diesel had the baffle separating the two fail. The load mixed and was used to fill the service station's premium tank. I ran it for about 10 miles out and 10 miles back to the station. It ran progressively worse until it would barely run when I got back. Siphoned the fuel out and refilled with premium at another station. I did a bit of research following the event because I had similar concerns. However, I found that diesel has lubricating qualities and, while it runs and sounds terrible, no damage should result. I continued to ride the BMW for another 45K without any issues.