On January 4, 1995, about 1115 central standard time, a Lake LA- 4-200 airplane, CFGDZ, sustained substantial damage during a forced landing near International Falls, Minnesota. The solo commercial pilot reported no injuries. The personal flight originated about 1100 in International Falls and was conducted under 14 CFR Part 91. The planned destination was La Crosse, Wisconsin. A flight plan was not filed and visual meteorological conditions prevailed. In his written statement, the pilot reported that he experienced low oil temperature and pressure about ten minutes after takeoff. He turned around to return to International Falls. About five minutes later, the engine "shuddered" and lost power. He executed a forced landing in a swampy area. Small shrubs and trees were encountered which damaged the wings, lower rear fuselage, and horizontal stabilizer. The pilot reported the crankcase breather tube was solidly blocked with ice and oil was expelled through the front seal. Federal Aviation Administration (FAA) Airworthiness Directive 64- 17-05, was issued August 28, 1964 and was applicable to Lake LA- 4, LA-4A, and LA-4P airplanes. The directive specified a modification to the breather tube by the incorporation of a "whistle slot" to preclude loss of engine oil due to icing. FAA inspectors who examined the wreckage reported this type of modification was not incorporated on the accident airplane.