Recently I bought a Mitsubishi OEM aluminum valve cover (p/n: 1035A810) and have it professionally installed. My main motivation is to prevent the aging plastic valve cover from leaking oil at the manifold side, and potentially causing a fire. The OEM aluminum valve cover comes with a new gasket. It's bolted to the cylinder head with specialty bolts, for which I bought the MAP titanium ones (p/n: EVOX-VCH-TI) and they have worked well.

The PCV valve and hose on the front are of the same size between the two covers. To prevent my old PCV valve from leaking boost into the crankcase, I bought a new OEM PCV valve (p/n: 1035A422). So everything here is plug and play:

On the driver-side, the aluminum valve cover has a 3/8" (9.5mm) angled breather bung facing the firewall. It's different from the plastic cover's 1/2" (12.7mm) straight breather facing the coilover. My mechanic had to order aftermarket reducer connectors (p/n: 28609), and to use a couple of clamps and a 3/8" oil-resistant fuel/PCV line in store to make it work. (Mishimoto also makes a 3/8" catch can hose. The breather hose difference would be a nonproblem for AMS intakes, which comes with a 3/8" bung installed and an optional 1/2" bung included.)

The wires have a lot of aluminum clips that cannot be simply moved from the plastic cover to the aluminum cover. Another Evo X owner Zijie He's guide "Up/downgrade to aluminum valve cover" helped. It took my mechanic more than an hour to fabricate and custom the clips.

Photos:


Old plastic valve cover. I used a Sharpie metallic silver marker to mark the ignition coils.


Wires sitting leisurely on the old valve cover without ever melting. It's Japanese sorcery.


Plastic valve cover (1035A999)'s 1/2" (12.7mm) breather bung.


Aluminum valve cover (1035A810)'s 3/8" (9.5mm) breather bung.


The OEM aluminum valve cover (1035A810) comes with an included gasket.


Aluminum valve cover freshly installed. Some wire clips have to be fabricated.


After taking these photos, I proceeded to wipe clean the new valve cover. I tested a handful of car care chemicals. It turns out that the good ol' Multi-Purpose Auto Cleaner works the best.


Gates 28609 3/8" to 1/2" reducer connectors.


Gates 28609 inserted into the stock intake hose (1505A304). There is some sort of stock rubber o-ring on the hose that makes this connection air-tight.


Plastic valve cover (1035A999) removed. So has been the stock intake hose (1505A304)'s 90° elbow for the 1/2" (12.7mm) breather.