There is no need to remove the original lap sealant unless the roof was dirty when applied and it is coming loose. Use a mild detergent/degreaser to wash the area, let dry and the new sealant can be applied on top of old.
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