aye diff was miss matching so rear wheels were going at different speed to fronts, quick diff swap and jobs a fish.
As far as the ratio being out it needs to be matched perfectly or you'll get issues that will destroy your diff.
Afraid its not, its pure luck. I know cars that have had 2 engines in 15k miles, some that were babied and failed but then also know some that were abused like a redheaded tiwanese hooker and are still going strong.
Here's the 2k long thread on SN about it,
https://www.scoobynet.com/scoobynet-general-1/828990-2008-2010-2-5ltr-engine-failures.html
It's just pure luck
If its any conciliation im kinda int eh same boat, my daily volvo went bang so now tryign to decide on a replacement. couple of hawk wrx's etates are available and im pondering on the 2.5 issues or leave it be
roughly 4.5k for a proper rebuild assuming no damage.
You could possibly get a hawk wrx estate forged, bigger turbo, suspension and brakes for that sort of money and it will be pretty bullet proof. But your gonna be at the top end of your budget. or you could take the chance on the engine.
Blob WRX would be cheaper option, engine will be fine at 300-350
http://www.pistonheads.com/classifieds/used-cars/subaru/impreza-wrx/subaru-impreza-wrx/7049555
You could take into account an engine refresh cost in the buying price? but tbh you'll find the audi or vw boring as sin. i went from a hawk wrx (although tuned to 400) to an e46 and it was seriously dull, really nice car but just dull by comparison
Ring land failure, head gasket failure. Not alot you can do, headgasket failure can be check with a snif test but will only tell you it has or hasnt failed and doesnt mean it wont fail 2 miles down the road.
Only real fix is rebuild the engine. tis ashame cos built right they are a cracking road engine
and look whats poped up on ebay,
http://www.ebay.co.uk/itm/2015-SUBARU-XV-I-SE-SYMMETRICAL-AWD-BLUE-SALVAGE-DAMAGED-REPAIRABLE-PETROL-4X4-/152486230553?hash=item2380e33a19:g:-IsAAOSwWxNY14Ku
when you get to MFN just park where your told to, isnt a stand or anything.
https://www.google.co.uk/maps/dir/53.0021541,-1.2820182/MFN,+Shipley+Gate,+Eastwood,+Nottingham+NG16+3JE/@53.0131301,-1.3198716,4398m/data=!3m1!1e3!4m14!4m13!1m5!3m4!1m2!1d-1.3029526!2d53.0168826!3s0x4879eb600c68b51b:0xabba9aa9142d365d!1m5!1m1!1s0x4879ec844553bb61:0x176becb45ba0f72e!2m2!1d-1.3132529!2d53.0029644!3e0?hl=en
Hawk box will be fine. I ran one at 400/420 for 18 months no bother. They are about the strongest 5 speed you can get. I'm or sure if the hatch uses the same box or not.