You can buy the small plug that leaks from Ford for £7.50,got one for mine yesterday. You get plug and seal but no spring clip,don't think you need to replace this. Some Ford garages say its not a replacable part and you need to buy a whole new thermostat housing but they are bullshitting,just after more money. Its a common fault to go on st170's but mine's lasted 5years so not that bad,just hope the new one lasts as long. Good luck..