Recently upgraded from a 1.6 zetec focus to an ST170, and already the ST170 is giving me problems. It appears to have a slight water leak from the thermostat housing, and also going from the oil and water temp gauges, the thermostat seems to be stuck open. How easy is it to change the thermostat on these? There's no haynes manual but is it the same proceedure as on a standard 2.0 engine (as covered in the haynes). I'm aware theres a common fault where an o-ring goes on the 'stat housing causing the small water leak... anyone else had this problem? Thanks in advance, Tim.