Nice that it has the 5-speed manual
However, it is well past the 100k miles mark, which we can easily assume the head gasket issue had already occured.
My car, 99 Legacy Outback, as the same EJ25D as that Legacy GT.
My head gasket failed me in the 92k to 93k mileage. There were absolutely NO SIGNS of the head gasket failure until I looked down the coolant reservoir one time I had nothing better to do. It was almost empty, and I could see vapors coming out the bottom of the coolant reservoir. So I filled it up with Subaru long-life coolant/antifreeze and hoped for the best. Turns out I caught the problem early, it was leaking rather slowly (after adding the Subaru cooling system conditioner). However, it did NOT stop the problem.
As long as it has the original gaskets, you're going to need to get the replacement gasket. Subaru has stopped producing the bad head gaskets and has made new gaskets that should be fine.