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Probably unrelated. May need a valve body soon though. Those early top-loaders have issues with TC lockup solenoids. GD

Not any more than anything else that's approaching 20 years old. A lot of mistakes and neglect can happen in that time. My '00 has been well cared-for, and I wish it would run warmer. Only on the hottest days do the coolant temps get above 180, when it's below zero outside, it barely gets over 160. I'm thinking about replacing the OEM stat with a cheap aftermarket one to let it warm up a bit. OEM SOHC headgaskets usually leak oil externally. Overheating is more often caused by dirty radiator, failed fans, plugged heater core, etc.

Yes. More often than not it's due to the headgaskets having already been replaced, cheap gaskets, poor quality job, etc, or someone limping them around with low coolant/other issues because the cars are getting older and lower value, hence more prone to poor maintenance, ignoring issues like coolant loss, etc. Failure modes expand once the heads are off and gaskets replaced. You're right, it would just be more accurate to say it this way:

We entirely disregard Subaru's recommendations on oil unless the car is under factory warranty. We average about 1-2 oil changes 5 days a week for customers - usually schedule these at 9am to get them out of the way and out the door. THE ONLY TIME we use anything other than 5w40 (or 5w50 for 400+ HP), is on cars that are under warranty obligation to use 5w30 or 5w20. Everything else gets 5w40 Amsoil Euro FS. This is an XL oil with a 5w40 spec (normal XL is 10w40). https://www.amsoil.com/p/sae-5w-40-fs-synthetic-european-motor-oil-efm/ It's rated for 12,000 miles. We run it for 6,000 miles since the WIX filters rate about there and Subaru's shear their oil and dilute it with fuel (especially the turbo models) causing some level of consumption after about 2500 miles and we can't trust most customers to check their oil. I'm quite sure that all our customers combined have 10's of millions of miles on this oil and we have NEVER seen a failure related to oil breakdown, sludge, or really any lubrication related failure other than customers that burn all their oil up or leak it out and cause mechanical damage from the complete lack of oil. I have torn down engines due to failures unrelated to the oil - in one case we pulled down a built engine due to a cracked cylinder liner - plugged injector from tank contamination caused a lean condition under boost and the high cylinder pressure blew out the sleeve. Even under the SEVERE detonation conditions that resulted in a cracked cylinder sleeve we saw ZERO damage to the bearing journals running 5w40 Amsoil. So I'm not inclined to change my process. And I have reviewed the specs of the new engines vs. the older engines with respect to bearing sizes and clearances and oil pump specifications, etc - there is no difference between the older engines that specified 10w30 and the newer engines that specify 5w20. Subaru changes the spec based on meeting emissions and economy guidelines, and changes the recommendations for different markets. They have in the past offered 40 and 50 weight racing oils with their branding - in other markets. Viscosity is chosen based on engine LOAD. Higher load requires thicker oil so it doesn't squirt out of the bearings under high cylinder pressure. Take note that I own and manage a performance shop - as such my customers are largely composed of "Enthusiasts" who often drive their cars at the hard. I myself drive all my cars hard and have blown up my share of engines personally. Hard driving equals high load. And thus a step up in viscosity is warranted. GD

Use synthetic. The end. Lol. If cost is a concern extend your oil change intervals as synthetic allows. But check oil level often. Brand and weight don’t matter if you want top shelf get amsoil and read GDs data driven commentary on past threads. You have a 2007, those blow the short block all the time due to oil loss/low oil, 10,000 times before they do due to weight or brand. Use synthetic. The end. Most info is short sighted, anecdotal and/or impractical and useless. Practically speaking it doesn’t matter, except use full synthetic for your control rings. Follow the owners manual for weight of that year 5W and 10w are both fine. Varying weights isn’t necessary but not a terrible idea either. Most responsible car owners with average daily driver commuters change their oil well before the oil is problematic. so it’s not like they’re being pushed to the limits where one brand will perform better than another Subarus are making 200,000+ miles all day long on whatever oil is on sale. And there’s people promoting every brand as awesome because some oil wizard told them about it and they’ve never had issues. Well join the club buffoons, that’s everyone, no matter the brand. Lol. And that’s why no one can resist talking about it - theyre guaranteed to be right, or partially right....because most of what people talk about doesn’t matter empirically or practically. I’ve never blown an engine and have driven a ton of Subarus past 200,000. Is it because of my meticulous attention and robust knowledge of oil? Good grief, no. They fail due to oil loss, low oil and neglect. Use synthetic to keep those control rings clean. your year is prone to low oil. Your best protection is synthetic, frequently checking the oil level and not brand or weight, beyond obvious guidelines. Those engines are routinely found with blown short blocks due to oil starvation not weight and brand. There is a small range where better oils will protect in adverse conditions like low oil where the temps and over cycling degrade the oil properties. But the range where that happens before it hits low enough oil to destroy and engine no matter what oil is pretty narrow relatively speaking. But still amsoil would offer some additional protection there.