The Northstars had some quirks in the design that made them a bit different from the equivalent Galaxy models. They were okay radios 20-plus years ago, but they haven't aged as well as the more widely-sold brands and models.
There were production changes from the first ones made to the last ones, as well. The first ones used a conventional channel selector, just like the Galaxy radios. Later ones replaced it with a computer chip controlled by a wimpy "encoder" to select channels. When that chip croaks, it's off to the junkyard.
There's a double whammy to first find someone familiar with those quirks, and then find someone who will agree to let you ship it to them for service.
Leads me to expect it would be expensive to have serviced.
Ultimately a truck-driving radio is still just a tool. What it's worth has a lot to do with what it costs you to make useful for the job it does.
My favorite comparison is to your favorite firewood-cutting axe. Eventually the handle splits. The hardware store wants 25 bucks for a new handle. But a whole, new chinese axe is fifteen bucks.
If replacing it is a cheaper solution to achieve the same result, the next question about servicing it would be "why?".
73