I am pretty sure that the 291 is just a sealant while the more expensive 292 is also an adhesive. In your case however I would be pretty careful, You don't want to just bung in a load of cotton and then sika over it, caulking is a pretty complex job and if the seems are very dry and open then if you shove in a load of cotton you might do more damage than good. The trad stuff (from what I hear here) to use is white lead putty above the water line and red lead below, sika would be easier to get hold of though and perhaps easier to use. We have filled in some small gaps in our caulking before with sikaflex both the 291 and 292( there was a patch of rot that had to be dug out between two strakes that evolved removing some timber and repair) but read up a bit on caulking and the like before you attempt anything big.