Please, do NOT attempt to disassemble brifters. That can only end badly.
Flush liberally with WD-40,working the mechanism frequently. T
hen blow as much of the solvent out of the brifter assembly as possible.
I am not sure what lubricant is recommended; possible some aerosol white lithium grease.
Clean and lube the cables/housings to eliminate internal friction and/or gumming up.
Good luck!