So that 2.5L engine family went through more tweaks than I can keep track of but between 2000 and 2003 the driver side heads were developing a weeping of coolant the subaru fix was pull the head put in an updated gasket re install etc. My 2001 at 64,000 miles started to get the drippy rear back corner driver side coolant leak. 180 miles a week commute I was maybe adding about 8ounces of coolant at the end of the week. It wasn't easily noticed given the hot exhaust would evaporate the evidence pretty fast. Basically you have to drive the car some, park with the front wheels cranked to the right, jump out peak under the car from just behind the driver side front wheel at the rear bottom driver side corner of the head to catch sight of a few drips of coolant. My car was at the dealer from 12noon to 12noon 24hrs head was pulled new gasket reinstalled etc. At 180,000 miles it was perfect zero leaks ran great. From about 2005 through 09 the leaks could often be oil instead of coolant due to Subaru changing the coolant path vs oiling system resulting in it being more common to see an oily mess due to weeping gaskets vs coolant etc. Keep in mind valve covers that leak on this engine can make a big mess and easily be sold as a HG failure to the unknowing when really its just a Valve cover that needs to be replaced. A very clean well cared for engine valve covers seem to start leaking around 150K. The other indicator of oil health regarding frequency of oil changes is the O-ring on the oil pump behind the timing belt cover driver side bottom corner. Poorly maintained 2.5's need that O-ring replaced at the 100K mark given its leaking oil by then. My car got Oil changes every 4000 miles typically synthetic and at the 100K TB service the oil pump looked brand new no leaks. The dealer told me in their area most subaru owners beat the crap out of their cars and are a bit lax on maint also and 80% or more typically need that oring replaced during the TB job. They also said its not uncommon to see the Valve covers starting to leak at 100K due to the same reasons. But a car with good oil change history 150K the valve covers will finally start to leak. Its one thing to haul trailers and heavy loads but keep the engine cool and operating correctly vs abuse the engine with bad oil cycles and over heat it etc. Heck my clutch even with boat towing and living in SF commuting all week the release bearing started to fail at 140,000 miles the clutch had 10% material left on it when I had it done. Full proper job bearings, plate and flywheel all replaced.
I'm 99.999% sure that most of the EJ engine issues come from folks #1 Driving them hot ie cooking the bottom end without realizing it. #2 not keeping an eye on coolant levels and yep cooking them again etc. I never had any issues with the car beat the living snot out of it but paid very close attention to running temps NEVER EVER!!! As in EVER!!! Ran it hot the second the temp started to move beyond normal I was in full temp management mode heat on full blast, slowed speed etc. The air flow issue through the cooling system also translates to it takes a little bit of time to stop the temp climb and get it back to normal. My Toyota Land cruiser the few times it started to show a temp spike you could stop the spike and cool it down near instantly by slowing up turning on the heat etc given the cooling system was just big and could shed heat fast. The subaru not so much it felt like forever before you started to see results regarding temps stopping the climb and returning to normal.
NASIOC is a good one too, though more Impreza-focused. Wikipedia and Edmunds.com can prove to be surprisingly detailed sources if you're looking for basic info about model years and different variations. Edmunds also has consumer reviews, though a lot of those people could stand to proofread and punctuate their posts a tad better.