Subaru_Lurker

I have been reading around the forum about the common oil leaks in the head gasket and valve covers on many Subaru engines. It sounds like the usual advice is that if the problem is addressed early enough, it's cheap to fix either DIY or at a mechanic and not a serious threat to the engine. But if the problem is left alone, especially if the oil isn't refilled, it can destroy the engine. That all seems reasonable, but I am not sure how to apply it to searching for a used Subaru--what can I look at to figure out if an oil leak is bad enough that it can't be easily fixed, or is so bad that the engine might start misfiring and fail as soon as I drive it away? I guess some people drive their Subarus around for years without doing anything other than adding oil, so is there any way I can tell whether a small leak is fine or is fatal?