A discovery paper today from PNAS:
Spontaneous generation of hydrogen peroxide from aqueous microdroplets
Abstract only: https://doi.org/10.1073/pnas.1911883116

The majority of dark slope streaks on Mars are dry cascades of dust. A few seem to last beyond global dust storms. They tend to show no relief but may brighten with age and show some small relief after completely fading.

A possibility is that a subset of streaks might be due to etching from a gas leaked from the apex where rock has been exposed, If the candidate gas was released water vapor from exposed subsurface, this new paper suggests that H2O2 can form without catalysts. As microdroplets get smaller, the process gets more efficient. New slope streaks appear during MRO surveys but so far none have been witnessed in the forming stage. An important constraint on Mars is that as the sun rises H2O2 is quickly destroyed. This may imply that formation may be before dawn making it hard to observe. If the etching produces heat,orbiting infrared sensors might see it. Length of streak might depend on water vapor volume, slope angle steepness, and how long before sunlight comes.