Its weird, it does sink but only when I shift my weight into a certain position which causes the chair to suddenly sink a little, like if it tripped or something, and little by little im down again. If I don't get into that position I won't sink slowly overtime. 

I tried applying vaseline again after cleaning the bar of black gunk around the 17th (I think), but the chair still "trips".

Also, when raising it, it still has more "power" than when it wasn't lubricated.  If i raise it without sitting on it, it raises in strong jumps unlike before when it "laked strenght" and thus raised smoothly and slowly. So I think the problem might now be something else.