IF you grease the gimble while turning it and see brown grease come out, replace it same with the u joints, if you see the grease coming out brown in color then water got in.
If you have salt deposits in the area where the bell crank sits (which is a known problem area on the Cobra) you need to check the drain plug on the side of the pivot housing (lower one on the same side as the bell crank). This was put in to drain water in case the owner did not pull the drive to prevent that area from cracking. Take out the plug, make sure that it still has the oring on it, if not replace it and coat threads with OMC gasket sealer. Clean salt deposits out, if the bell crank has the grease fitting on the side, grease it well, if not grease it by hand with OMC triple guard. I also pack that whole area behind the bell crank with it. Then when you re-install the drive clean the mating surfaces well, coat both sides of the gasket generously with OMC gasket sealer, and the mating surfaces too. Doing that every year, I have been able to keep water out, no shifting problems, mine shifts out of gear with 2 fingers on the control. I have replaced the bellows 2x in 17 years of ownership, gimble once (in 2005 still fine) and the ujoints are the same ones on it when I bought it.