Can 4Trak owners please advise - Gear selection becomming more scratchy as oil warms up. Local 'experts' recommend using standard SAE20W-40 type motor oil instead of prescribed SAE 75 - 85 since temperature rarely drops below 10 deg Cent. in South Africa. I'm unsure if this is advisable. I've added 'Prolong' to boxes to evaluate, found negligeable improvement. Checked mainshaft nut on back of Transfer - still tight. How safe would it be to decrease the viscosity for reducing the scratching gear change?