Well, no sense arguing now - the car is sitting in my garage! Thanks for all the prompt advice.
It was the real deal - no question about the mileage being genuine, and the oil was indeed 19 months old (ie the dealer had not changed it just for the sale).
The oil was a healthy brown (certainly not black), and the level was sitting just above the full mark. Still good viscosity, (not overly runny and not thick or sticky) and perfectly 'fresh'-smelling. I had my trusted Subaru Service Agent on the phone (NB not a stealership, but an accredited independent), and he was not at all concerned about what I was describing to him. The coolant, ATF and other fluids also looked fine. I didn't really have time to hang around for oil analysis results, so I pulled the trigger.
After all, we have machinery on the farm that can go a couple of years without an oil change because it does limited hours. No oil analysis has ever indicated that it needs changing sooner than what the engine-hours would suggest, and it mostly does heavy-duty work whenever it is running.
The 5-year warranty is the original Subaru Australia extended warranty. I can have it serviced at any Subi service centre (ie my accredited independent). I double-checked with Subaru Australia using the VIN code, and the balance of the warranty (a whisker over 2 years) is transferable to me just like a normal 3-year warranty would be. I'll run the UOA, just so I have something to fall back on in case it ever comes to a quibble over servicing intervals.
I paid $31k (+stamp duty) for the car, and couldn't be happier. I drove it the 500+km home up the twisty, mountainous road and all I can say is f*****g wow!! No family sedan has the right to handle or perform like that!! I thought our Gen3 RX handled ok, but this thing just looked at the twisties and said 'meh, what corners?' I can hardly wait to get it serviced and take it out for a proper run
Oh, and the oil level did not drop perceptibly on the run home, so it doesn't seem like it had been unduly diluted with volatile elements.
Warning: Dodgy mobile-phone pics to follow:
Thanks for the help, guys