I've had my Nav 750 since 2000. I liked the idea of docking stations in the different vehicles and just transfer it over as needed. I originally bought it for a 2000 Excursion I used for towing a TT.
About a year ago just before I went to Alaska I took it to the dealer that installed it for updating. He sent it to Magellan and for about $100.00 or so they updated it. It works great.
The model Nav 750 I have is like the ones they use on the rent a cars. It has a portable hard drive brain and a portable handset screen; they are transferable from car to car.
Your best bet is to call them directly or find a dealer. Good luck.
Just for the heck of it I did a search on the Nav 750 and found one on E-bay starting bid at $9.99. Nav 750
Maybe your better off buying a new one.