You’ve got that right.. the engine must be partially removed to allow access to do the job. Grrr....
That's because that is what usually results if you fail to notice the start of the discoloration of your coolant reservoir. As the gasket starts to fail engine combustion gasses/oil contaminate the coolant till total failure/overheating result. I was considering a Forester at one time. My SIL bought a used Forester. I knew about the head gasket issue and decided to wait and see if the problem had been resolved. It wasn't. End result a $3500+ engine replacement.
http://www.smart-service.com/blog/2010/02/subaru-head-gasket-will-subaru-pay-for-repair
http://allwheeldriveauto.com/subaru-head-gasket-problems-explained/