Unfortunately, Garmin's 'one-price' flat-rate exchange is a bit of a con. For example, a 'one-for-one' exchange refurb 3790 costs AU$199 plus cost of shipping the old unit to them. It must be complete in parts, even if the screen is smashed, PCB cr@cked and the case damaged 'coz it's been run over by your 4x4 in rocky terrain. The catch is that if you know what the 2nd hand value is, you can buy a pristine 3790 for half that on eBay. Sure no 3 months warranty, but wot-the-heck ... half the price, you get duplicate accessories and still got your old unit for spares.
PS: Don't worry Ol' Timer. I won't delete this time, but best look after those brain cells a little better hey?