Civi wise we had an expensive artificial horizon fail, looking in the back the filter was clogged with little black particles, a warranty exchange was arranged and installed with no problems, the company then refused the claim as the filter was contaminated so must have been done at fitment, fine says me, but you fitted it 4 months ago when you built the aircraft. Ahhh ermm warranty accepted and Service Bulletin arrived a few weeks later for everyone to check theirs for contamination.