The zoom ring on my 70-200 2.8 feels just a little gritty. Looking at the lens rental teardown of the lens, it looks like it's pretty easy to disassemble the lens to the point of getting the zoom ring off to clean/lubricate it. The thing is, I can't find a definitive answer anywhere online as to what the proper grease is to lubricate the moving parts. Does anyone know what Canon recommends for this? Some sort of lithium or teflon grease?