Straightening valve

Well, it's been a while since I've been on here. The car has 25,000 km on it and runs well, although it's using or leaking coolant, and it overheats when the coolant level is low. The thermostat is fine, the fan and radiator are clean, and everything seems fine; it's just that it's using or leaking coolant now, but I don't know where it's coming from.

I'm about to buy a Seat Leon 1.9 TDI with 105 hp and I was looking for a workshop manual for this car. Does anyone have one?