On September 30, 1998, approximately 0945 mountain daylight time, a homebuilt Mayala Dragonfly, N4478V, registered to and being flown by a private pilot, was destroyed during an emergency landing approximately one mile north of Avon, Montana. The pilot sustained minor injuries. Visual meteorological conditions prevailed and no flight plan had been filed. The flight, which was personal, was to have been operated under 14CFR91, and originated from the Helena Regional airport, Helena, Montana, approximately 0915. The pilot reported that the takeoff, climb-out and level off were normal but that "about 25 min[utes] into [the] flight, [the] oil pressure started down. It went to zero in a minute or 2" and that "the oil temp went up." The pilot initially evaluated and then discarded landing on highway 2 due to numerous vehicles and multiple wires crossing the highway. He then maneuvered to land on highway 141 but determined that once again power lines interfered with a landing along with a curve in the highway. He then elected to land in a pasture. The pilot reported that the pasture was rough, and that during touch-down "the right main hit a (hole, ditch?) bounced up & the canard (left) hit the ground & started the craft to cartwheel" (refer to CHART I). On site examination by an FAA inspector revealed a considerable amount of oil on the aircraft's belly, but little if any on the windscreen. The firewall was covered with oil, and the engine sump oil drain plug was observed in place. The pilot/owner reported that the aircraft's Volkswagen engine rear crankshaft seal "chunked and rolled up," that the "neoprene part [was] gone," and that "all [the] oil [was] pumped out during the 30 min[ute] flight."