Everything works fine on this old system except that I have intermittent funtioning of the speed readout. It reads 0.0 most of the time although it has worked properly on prior outings. I checked the knotmeter on haul- out and it spins freely. Does anyone have experience with this system who could steer me in the right direction? I check SR Mariner''s website and they sell manuals but I did not see the Nav 10 listed. Tim