Serpentinisation on Earth
Tends to produce Hydrogen seeps. Perhaps on Mars, this would react with atmospheric CO2 to make methane+water. On Earth, it reacts with Oxygen to make water. Not quite sure what you're saying (or that Lisa Pratt is saying) about plugging things up. This might be a specific situation in Earth's deep oceans where clathrates form. The lower pressures on Mars and lack of surface liquid water may make things a little different, maybe.
The REALLY nice thing about Mars is that it's a whole new planet, and things happen a bit differently than on Earth. Our standard experience and assumptions don't quite apply and we have to think REALLY carefully what *might* happen.