I have a 1998 Subaru Legacy GT with 243,000 km on the engine. The car is in mint condition - arctic white paint. The head gasket now needs to be replaced. Did all the maintenance. I've been lucky it lasted this long. Car was mostly highway driven. Car is drivable and the leaking coolant is gradual and would go un-noticed to someone not familiar with the car. Head gasket is not reliable so getting it replaced by a certified Subaru mechanic. Will cost $3,500 to do it right. Don't recommend to do it cheaply because if its not done right the gasket can leak again.
Link that provides excellent info about problem:
The all wheel drive system is excellent.
Head gasket and cooling system design.
An interesting read on cooling design problem:
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