Manual Steering Gear Box

[Mullett]

My gear box has a slow leak and I want to keep it lubed. The shop manual says to use SAE90Ep - the closest thing I can find is Castrol Gear Oil SAE 80W-90. Is this good to put in there? Don't know what is in there now - is it ok to mix? if not how do I drain it? If so to fill I assume I just remove the plug on top and filler up?

 

[NoJoe]

It wont hurt to mix, and I use 85-140 but the 80-90- is fine.