Are they actually gummed up, or do they have the common tendency for the small lever to drag the big lever along, causing lockup i.e. failure to shift?

The most common failure for all of the 9-speed levers, aside from the lesser models gumming up, is breakage of the tips of the anti-carryover latch mechanism, which no amount of solvent or lube can fix. The latch normally prevents the big lever from moving when the small lever is actuated.

But if the levers really are only gummed-up, there is a lot of market demand for right-side levers from the 9-speed series. I am always running out of such shifters to sell, even if I have to soak them in 170F motor oil to free things up.