(I'm trying again because my first attempt at responding apparently
didn't work... but if you see two different responses, that's why!)

In my experience, opening up both chambers of the cassette and giving
the pieces a quick wash in cold water, then letting everything dry
completely before reusing the cassette, works just fine. I've never
seen any evidence of the light trap decaying due to the chemistry.

In fact, the main cause of cassette failure is the thin bridge-piece
breaking when I'm bending it too far during sliding the film into the
light trap when loading the supply side chamber. I've also had the
bridge-piece break when getting a somewhat stuck cassette out of the
camera.

I've reused some cassettes as many as eight or ten times, but that
thin bridge-piece always eventually breaks - it's the Achilles Heel
of Minox cassettes!