I wouldn't necessarily say the coolant leak means it's been driven low on coolant. Mine had a tiny leak from that gasket for a while but the effect on the coolant level was very slight. I replaced the thermostat and gasket and it hasn't leaked since, so I'm guessing it was the gasket. On this guy's car, it could be a gasket, improperly tightened bolts, warped housing, lose hose on the housing neck ... I'd check out how "minor" the leak is and go from there. At least the guy seems to disclose the car's problems rather than the usual sugar-coated ad. Given that it needs a couple things (I wouldn't last long without a blower motor, and a speedometer is nice to have), I'd probably try to talk down that price. Especially if it has rust, too.

__________________
1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)