I used to work for a guy that modified Subarus. We would get unmodified cars in all the time for head gasket/cooling leaks, specifically the 2.5L. A couple times it was bad enough to hydro-lock the block, requiring a completely new short block. Not a cheap repair, if I remember correctly it started around $1300 and could go way up from there if you needed a new short block (and that was us, I don't know what a dealer would charge).

Once that was fixed though, they were great engines. We had a couple WRX's that we replaced the block with aftermarket one, then we would add a larger turbo (with controller and injectors), turbo-back exhaust, front mount inter cooler, a stronger clutch disk, and tune them on the dyno. The cars would run 400+hp no problem as daily drivers.

They were stupid fast from a dig, a lot of fun to play with.