Are you suspecting that this engine had a massive impact in the past?t Or this is a metal fatiguing issue that should be covered by Subaru?
If I were you, I would start collecting info about similar issues online. I'll also speak to someone in the dealership without taking the car for inspection. I'd exhaust every possibility for the root cause of this before thinking of how much I should start saving!
This has just reminded me of the last Subaru mail I received last month talking about possible cracking in the steering system!
Oh.... Well I'll keep an eye on it every oil change. If oil is coming out of it, then it's time to worry. For now it doesn't seem too bad. I would plan for the worse just in case it goes south sooner than expected.
Alluminum cast in sand molds often picks up even the crack line of the sand mold, like some concrete shows the grain of the wood used in the forms. You could take a file or sandpaper and just file or sand down smooth a section to see if the line vanishes or not. That smear looks almost like cured JBWeld, possibly was someone thinking they were covering a leak as seapage will sometimes follow those lines.
The area under consideration looks like it is a big 'block' of aluminum where a couple of 'legs' come together and get a bolt through it. This area is going to be thicker than anyplace else. What I would be most concerned about is a crack around where the bolt goes through. Or where each of the legs come into the 'block' of metal. It's not likely that the whole 'block' would shatter.
I'm going out on a limb but i sent the photos to an actual metallurgist who does failure analysis on aluminum structures (aircraft) he does not think they are actual cracks through the block, but rather cracks in a coating or casting cracks as someone else suggested.
I was thinking, which is not always a good thing for me. I've done a thing elsewhere that goes like this. Find a crack. Put a thin coating to lay over the crack of something like JB Weld. Let it cure completely. If the crack comes through the epoxy at some future date, you know you have a break under the epoxy. If the crack doesn't come through, you know it is just a surface blemish. The thin coating has to be kind of brittle because we want it to crack to indicate. If it's too soft, it will just stretch with the metal.
In case anyone is curious, the standard test for evaluating possible cracks like this is a dye penetrant test. It’s not something you or I can do reliably, but it’s what industry frequently uses to identify surface cracks in castings, welds, etc. It’s relatively inexpensive, by industry standards, but still out of reach for most of us. Google if you’re interested in that sort of thing.
Wow, you guys rock! @hertfordnc you're a genius. It took some finger gymnastics, but I managed to put my hand down just far enough with a sandpaper to remove a thin layer. Below is the before and after pics. As you can see, the "crack" lines totally disappeared in area that got sanded down.