Forester piston slap - long term effects

I've 50,000 miles on my 2002 Forester and the temperature that the piston slap becomes noticable has seem to rise from the 42F degrees that it originally seemed to be to seemingly all the time. Even in warm weather I have what I would have previously described as a lifter tapping. I have the 80,000 mile extended warranty and had intended to keep the Forester until "the wheels fall off", as I usually do with my cars. I can live with the noise if it won't shorten the life of the engine but am wondering if I should make a demand for it to be fixed? It doesn't use any oil between changes.