i would go for it if problems are fixeable.

 

I saw the item you're referring to on ebay. You can probably find a knob from another device that will fit it. However keep in mind it will probably be time consuming and it's not guaranteed you'll find it. As for the dealer I don't think they will sell just the knob.

 

checked with dealer and supplier of navi device...you can get a knob....buy it already.