The 5000 and 6000 used the same course computer back then anyway (IIRC). From your description it sounds like something funny is going on in the course computer. If the rudder moves when you hit the + or - buttons but the display does not change I wouldn't trust it. In addition to the rudder control on the pad there is a second one on the course computer below the heavy wiring. I do not remember which control takes precedence. If turning both controls to maximum does not steer the boat it is time to scrap it.

That chain drive is also the earlier generation. Before leaving the Great Lakes I suggest you replace the whole shebang.

If you do scrap it, I am interested in the servo amplifier board in the course computer to fix one of my spares.

I have a Raymarine S3G and and an Autohelm 6000 set up hot switchable. I did this because of infant mortality issues when I bought the S3G. I hope Raymarine, under it's new ownership, has cleaned up it's act.

PS. I got your email.