Interior leather dusty and moldy

[Max de CLINT]

Never had a lot of experience detailing cars before but I have picked up a neglected BMW that's had a water leaks then to allow the wet carpet to dry, its been sitting in a dusty garage with the windows open. The leather eats are filthy with a moldy dusty grunge over it, but looks basically sound. I use Oakwood Leather Care kit with the leather cleaner and hydrating cream but I'm wondering if there is a different product to preclean the crap off the seats first.

BTW I have vacuumed but the grunge doesn't lift.