The aircraft had been fitted with a tailwheel conversion prior to being imported from the USA. During a touch and go landing, the aircraft was decelerating in the three point attitude through about 20 knots, when the pilot lost control in a violent swing and wing drop to the right, followed by an immediate reversal to the left. The right maingear had separated from the fuselage during the landing roll. The maingear locating bolt and saddle bolts had been fitted incorrectly and were threadbound, allowing the gear leg to place abnormal loads on the saddle. It failed progressively until final overload failure during this particular landing. The aircraft had flown only 13 hours since being placed on the Australian Register. It was imported with the main gear undisturbed. The progressive mode of failure suggests that evidence of impending failure of the saddle should have been apparent for some considerable time.