The spool set will push out the assembly tool guide. The O-ring are now in position. (18) (780-3A) 5-81(3) (19) Turn the steering unit until the bore is vertical again. Put the check valve ball into the hole indicated by the arrow. (780-3A) 5-81(4) (20) Screw the threaded bush lightly into the check valve bore. The top of the bush must lie just below the surface of the housing. (780-3A) 5-82(1) Grease the O-ring with mineral oil approx. viscosity 500 cSt at 20 C . (21) (780-3A) 5-82(2) 5-41