After a minor shunt into the car in front at 15 mph max, the car was driveable and seemed OK, but 50 miles later smoke poured from bonnet due to oil spraying onto exhaust. Vehicle trucked to insurer's repairers who simply cannot trace the oil leak. Oil was 1/2 full on dipstick, but car serviced 8 weeks earlier. Engine steam cleaned and test run but still no signs of leak. Compression test OK so not head gasket. No oil pump as petrol. Repairers expect me to take back the vehicle and hope for the best, but once I sign off the repair as OK then if the leak recurs I will be responsible. I do not believe the oil leak was not connected with the shunt. Any ideas as to the cause/source of this leak?