Changing grease in manual tranny 86 toyota 4x4

there are 2 plugs on the side, not sure which one is the add one.
One has a star head & the other has a hex head.I think it is the one in line with shifter but not sure. I'm replacing with 75-90 syn. Is that a good choice & how much does it hold. I'd bought some mobil-1 GL5 but after some research it showed to cause damage to tranny. So the only thing I could find was some Coastal brand the specs of GL3,GL4 &GL5 syn.

thanks Mike or ''GRASSHOPPER''