Light is always leaking into all the canisters, so I'm keeping it all in a black bag after cutting it and rolling it into canisters. First three frames are usually a waste. The only exception (less light leaking in) was with a reusable spool with tight, wide padding of black Velvet.
So, the stronger stronger light-piping effect you observed was with single-use cassettes?
That is strange as the light piping effect should be independend of the kind of seal.

