So I have Lucas marine grease in brake slack adjusters for a little less than 12 months and the old grease coming out in kind of dark brown olive color. Should I keep using it or switch to some other grease?
It's just the grease getting mixed with dirt, salt, brake dust, you name it. If it's on the road it gets in there. All you can do is grease more often.
It's normal. Some of our trucks are greased every month or more and the grease will have some color to it but even the Schaeffer 219 I use looks like that after a long time.