My Montana 650 is also not working as it should, the screen calibration has gone haywire.
If you have to type the name of a street, it randomly selects a letter to the left or the right of that letter on the keyboard.
If you do the screen calibration, the calibration never stops, as if it's looping all the time.
I need to get the device to Pauli at GPS4Africa (where i bought it), but as this is a fairly old unit, I guess I'll also be offered a replacement unit.
Definitely not going to fork out R9999 for a new unit. Using a 276Cx now along with my two old 276C models. (Still the best GPS in my books)

Not sure what is available around the R5k mark that is worth buying.