Transmission Fluid In 850 Primary Case???

I am about ready to start my buddies 850 after doing a top end job on it. I was checking all fluid levels before startup and noticed something wierd?? The Clymer manual I have says to use 20W-50 oil in the primary chaincase. When I checked his it appears to have transmission fluid in it?? Whaaas--up?? Is it OK to use transmission fluid in the clutch primary or did he screw up and put the wrong fluid in?? If he did should I drain the primary completely and clean everything before adding 20W-50 or can I just remove the primary cover and re-install it with the 20W-50?? Thanks for all the great info!!

The original recommendation would have been to use motor oil but ATF now seems to be preferred by many Brit bike owners for the primary chaincase, except maybe for the 850 MkIII as they have a hydraulically damped primary chain tensioner that needs a thicker oil than ATF to function correctly.

when I was at Norman White's a coupla weeks ago getting my gearbox looked at, he told me to use fork oil topped up with a wee bit of engine oil.
millard