Few other things worth checking, problems I've had on my ST24, check rear wheel well in boot as water can leak round rear lights in to boot. Also check central locking all working as door solenoids can pack up.

You may hear scare stories about water impellers breaking, but this on early cars, which had black plastic impellor. I changed mine for metal impellor, but it a late model ST24 and it had cream coloured impellor, probably same on ST200s.

Problems I've had more annoying than expensive, I know not a ST200, but still relevant.

Hope you find a goodun, they are great cars.