The right main landing gear collapsed on landing rollout. Initial examination of the airplane by the FAA revealed the right main landing gear shock absorber had failed. Examination of the components by the NTSB laboratory revealed the manufacturer had not applied sealant on the internal surface of the cylinder nut in the radius area between the threads and the flange before the nut was assembled. This resulted in stress corrosion cracking of the cylinder nut, and subsequent collapse of the right main landing gear.