There are a few around Perth that were brought in from the east, as there was big storms in Melbourne that damaged cars last year as well
Some are 09 onwards so technically should have new car warranty.
If the car has been submerged above the door sill, eg, the bottom of the doors, the warranty will be voided.
As said above there can be no guarantee that electrical systems wont suffer long term damage.

If you buy from a private yard, do your research, ring Subaru with the VIN and ask where the car came from and when, smell the carpets, even carefully pull one corner back and look for a tide mark.
If they've taken the car to a dealer for repairs, it may be flagged in the database as stormed damaged.
I know of one black MY10 WRX and one MY10 GT LIb that are around Perth with a voided new car warranty, they were for sale from a private yard, the people that bought them may not even be aware.
Buying from a Subaru dealer will not be an issue as most of their cars will be SUbaru assured.

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F.B. Racing
01 WRX (STI badged)
2010 XR5 Focus
06 Impreza Hatch 2.0i