Oversteer would be associated with the rear pressures being too high compared to the front, which is the "odd" way around (usually, with the front wheels being driven and doing the majority of the work during cornering and braking, you'd expect the fronts to spiral upwards if anything)
Knackered rear shocks are a very common cause of oversteer. Look for signs of oil leaking from the damper. If you feel like removing the shock, then check that it "springs" back after you compress it.
EDIT: Oh and not forgetting the obvious, old tyres (grip is reduced through all these heatcycles, so it's not all about tread depth) or worn tyres etc.