Outgassing - no. In my view that would be pure speculation. The problem with outgassing is it is rare (only 7 known MB objects have exhibited this behaviour) and we would expect it to occur randomly and over a very short duration (months only) after some sort of collision with another body (also rare), it's not like there would be a sufficient 'localised source' that would act over a period of My to dramatically slow the spin rate. Mind you it will be interesting to measure the spin period for 596 Scheila after its current activity is over to see if there was any impact though it's current spin period determination is not well established.
Break up of a larger body would be the result of collision and thus expected to induce tumbling rather than 'simple' primary axis rotation which appears to be what I have observed.
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