Any vehicle of this age has to be approached on an individual basis. It’s likely to have covered a lot of kilometres by now, so any major (or minor) component could be well past its best.

Any Subaru transmission that doesn’t shift properly or is slow to engage a gear or shudders under acceleration needs to be either investigated further or avoided completely. Don’t forget that the Liberty was all-wheel-drive, so that places extra strain on the transmission as well as making for a more complex arrangement if it does need to be repaired or replaced.

In high-performance Subarus (such as the WRX) the transmission was something of a fuse if the driver got a bit over-enthusiastic, but in models like the Liberty, the four-speed automatic was a sound unit. When test driving the vehicle, make sure there are no thumps or vibrations when the gearbox shifts down, and try to shift gears manually. The gearbox should respond instantly to manual input, without any hesitation or noise.

I would use the factory recommended oil, at least while the car is under warranty. Once the warranty has expired you could use the Mobil oil and shouldn’t experience any problems.

In going order it’s worth $7000-$9000 depending on condition, so you have to consider if it’s worth spending $5000 on it to get it back on the road. It’s eight years old, has done 180,000 km, it’s probably best to sell it to a wrecker if you can get $2000 for it.