i've had mine 12 months now and i can't think of any bad points to ownership, there's plenty of stuff to check though before buying one.
service history is a must, mileage wouldn't worry me as long as it's got a FULL service history. a VAG history is "alright" but specialist servicing such as MRC or Star performance is prefferable, mainly because the dealers don't see many of these cars and don't check them for fault codes as a matter of course. it's all to easy for a main agent to miss some of the common failures such as the throttle body boot or F pipe. most owners are knowledgable enough about their cars to service them themselves, if that's the case check that they own or have access to a Vag-Com, you can't look after one of these without one. some well chosen questions should be able to sort out the enthusiast from the dummy. i wouldn't discount buying a car that has been serviced at home as long as the points above could be proven.
before buying insist on scanning the car with Vag-com. we negotiated a substantial discount just before xmas for a mate who bought one on the strength of a vag-com scan that showed a fault on the re-circ flap on the air-con and intermittent faults with the ABS system.
brakes can be expensive so make sure there's plenty of meat on both pads and discs, if not then either insist on them being replaced before sale or again, negotiate a discount.
check the tyre tread, and not just a quick glance, many S4's have been lowered but not had the camber adjusted accordingly which can scrub off the inside edge of the tyres so get undernieth and check the full width of the tread, whilst you're under there check the exhaust hanger behind the rear axle is still attached, these snap off, it's a common fault but an MOT failure.
look for the highest spec you can, ideally you want to find a facelift car with sat-nav plus, recaros, carbon trim and a sun roof then haggle like a 5 bob hooker at last orders. facelift cars have slightly better brakes and the RS4 exhaust manifolds rather than the early S4 ones which tended to break up which was like sending an RSVP inviting the turbo fairy round to party.
there should be no rust present whatsoever, these cars are galvanised from the factory and any rust is a sure sign of poor accident repair, walk away.
there should be no oil leaks, especially from the back of the engine, this could be rocker cover gaskets (easy) or turbos or oil lines (a bitch) so make sure you know what you're getting into and do the 5 bob hooker thing again, but this time it's 3 am and all the punters are getting taxis home.
turbos. there's really no hard and fast rules on turbo failure. some fail early, some not at all, it all seems to depend on the way they're treated, if the car has been thrashed from cold or switched off after a fast drive without being allowed to cool then you almost guarantee the turbo fairy will be knocking on your door. same goes for running on crappy oil and make sure the after-run pump for the cooling system is working too. and don't forget the F-pipe and TBB as the turbo fairy LOVES boost leaks.
remember, the turbo fairy is not our friend
but if you buy wisely, service it with care and replace the known weak points you'll be buying the most fun you can have in a car short of inviting Lindsey Lohan for a naked moonlight drive accompanied by nothing but a family size tub of chocolate body paint
