DETROIT, Michigan - Kawasaki US is recalling nearly 4200 Ninja ZX-10R motorcycles in the US because oil can leak on to the rear tyre and cause a crash.The National Highway Traffic Safety Administration says in documents on its website that the recall involves bikes assembled between September 1 2010 and February 15 2012.CRANKCASE SEALThe documents say oil can leak from the crankcase and pool. Continued use could cause the oil to spill on to the rear tyre. It was unclear if the problem had caused any crashes or injuries.Kawasaki US will notify owners and dealers will seal the crankcase to stop the leak.A spokesman for Kawasaki SA explained that the leak was actually from the starter motor and caused by a casting flaw allowing oil to sweat through but only one machine in South Africa has reported the fault out of about 160 machines sold."We will repair the fault on a case-by-case basis should any occur," the spokesman added. "Obviously anybody with an oil leak will take his bike to a dealer and we have a putty kit to hand to repair the seal."So, check our Ninja from time to time - just in case!