@MHC
Best not to guess the HWID. Usual chipsets in EU, US, AU etc are 0827 ('non-MTK') or 1091 (MTK) and you should check to ensure you use the correct one. Do as Caty says, or, you can get it another easy way from a backup via the device XML file. Browse the Garmin folder, look for 'GarminDevice.xml' and open it with a web browser. The HWID is shown near the top, look for the 4 figures 'PartNumber':

-<Device xsi:schemaLocation="http://www.garmin.com/xmlschemas/GarminDevice/v2 http://www.garmin.com/xmlschemas/GarminDevicev2.xsd">
<Model><PartNumber>006-BXXXX-00</PartNumber>
<SoftwareVersion>760</SoftwareVersion>
<Description>nüvi 265W</Description>

That also shows the firmware version immediately after the HWID, in example above it's FW v7.60.

In a healthy working 265W it's even easier to get it from the Diagnostic Menu: Press the battery icon (if charging, press just to left of clock) for about 5 seconds, press 'Next'> 'Start test'> 'More'. The first 3 entries will show which chipset (HWID) you have and the fw version immediately behind it. Or get the Device XML directly.

So many ways to find the HWID that it's almost confusing (in a good way).