There are theories here about the possible reasons, including geometry (higher suspension travel leading do different forces acting through bearing etc) and use of bike (Only old men ride RT's )
Not tried water, is it better than gear oil? Mine has not got hot, even after 200 miles on German autobahns. Cant see using Viton seals would help.(re another post) If the F drive is getting hot it's buggered. Mine is pretty cool, leaking, no wheel play but makes a cluncking noise when wheelis spun. Still had a great ride around Northern Ireland country roads today.
They are improving them though last one went at 6k on an 06 plate latest bike an 09 it went at 9.5k. Mechanic said the 2010 models are slightly different internals so hey maybe even 15k possible!