Being from Florida we became educated on mold. Mold can grow anywhere there is a source of moisture, stagnant air, and lack of sunlight. You can certainly breed a toxic mold in a motorhome too. I would recommend you do as you have said. Take out the area that is stained and repair leak, check to be sure no mold has started; if so kill it and repair the area effected. You might want to seek some professional or governmental advise as to what kind of mold you might have found and ask how is the most effective way to rid and clean up this strain of mold.
Mike, RVIA & RVSA Certified Master RV Technician
Amy, Dr. Assistant - Roxie & Mei Ling, four legs each
2000 Gulf Stream Scenic Cruiser 450 hp & 1330# torque
06 Saturn Vue, 06 Chevy Z71 4x4 & 2014 Corvette Z51 M7