Engine Rebuild
This will be an interim update with no pics.
I've finally joined the Subaru Club properly by having a head gasket issue. Both drivers-side cylinders (road/exhaust) side as it turns out. The symptoms were pushing a load of coolant out at the last Dirt Day, although there has probably been a mild head gasket leak for some time on account of the slightly scummy coolant overflow water.
The engine had been consuming oil for a while, so a bottom-end freshen-up is also needed if the heads are coming off.
There was a fair amount of carbon deposit in the combustion chamber from the oil-burning. The bores are in excellent condition however. Presumably we're just looking at oil control ring wear/failure. Pistons haven't come out yet, so ring land condition TBA.
After considering the options, I went for a factory brand-new EJ257 bottom end.
Despite the weight of opinion I went against a forged pistons option due to the fact that it's a daily driven car running factory-ish boost levels and knock-resistant E85 fuel. Also, the rarity of the lower-expansion 4032 alloy pistons would have added a month to the whole process.
I'll add an 11mm oil pump, some aftermarket sump goodies and other minor freshen-up old-for-new replacements for hoses etc.
Heads are being reconditioned and will go on with ARP head-studs.
Lessons so far
1. You do indeed need to run upper-engine cleaner in a car running full-time E85.
2. The catch can/s are certainly not 100% efficient at scrubbing the oil out of the blow-by gas. I already knew this from the clear hoses and intercooler contents, but it's interesting seeing the cooked oil residue in the inlet manifold. When my budget recovers in the year 3000 it's tempting to add additional catch cans in series to try to scrub the air more. Having said that, a brand-new hypereutectic-piston bottom end might have significantly less blow-by.
[probably to add to this list as the process continues]