I don't know about the unicorn discharges, not having had to obtain one, but Model 51 parts are hard to get, which is why I usually advise against shooting them. The most common problem is broken grips, a result of people trying to pry them off. (Grips are available today - the plastic part - and the metal can be swapped over.)
As a FWIW, many writers have tried to explain why the Model 51 was made with the separate breech block. The actual reason was that the idea of a one-piece slide and breechblock had already been patented by one John Browning, so poor Pedersen had to try to work around JMB's patents. (Browning had also patented the idea of using screws to attach auto pistol grips, hence the Remington's complex system.)
Jim
As a FWIW, many writers have tried to explain why the Model 51 was made with the separate breech block. The actual reason was that the idea of a one-piece slide and breechblock had already been patented by one John Browning, so poor Pedersen had to try to work around JMB's patents. (Browning had also patented the idea of using screws to attach auto pistol grips, hence the Remington's complex system.)
Jim