Brian, Thanks for your input, and yes I do agree with you, a lubricated thread is best for accurate torque settings, in this case my enquiry related to lubricating the bearing surface of the C20 nut, but I did not make myself clear. I don't use a torque setting for the C20 other than the FT torque setting.
A little unrelated, but in a conversation with Hugo Myatt yesterday, the subject of tightening the C20 nut was discussed, both Hugo and I are running Grosset electric starts, and Hugo suggested that it is a wise precaution to drop the starter motor out of engagement when exerting a tightening force on the C20 nut to avoid any damage to the starter sprag clutch and gears.
Does anyone have any other advice on this, Francois Grosset fitted my starter, and it has been excellent, does anyone out there remember getting any advice on this possible problem when working on the clutch.