Originally Posted by
AlwaysBeCycling
It sounds like the grease has gummed up and left the pawls stuck. You just need to take the shifter apart, remove any pawls, de/regrease them and put 'em back. I don't think anything's broken.
BAD idea on an epic level. Try spraying with WD-40 or other chain lube, but never try to disassemble a Shimano brifter.