Subaru engine oil leak causes -

So I have a 07 Subaru legacy outback wagon.

I bought it with body damage and I spent a good amount of time pulling the frame and what not.

It also had an existing oil leak. And over time, it has gotten pretty damn bad. So bad, my engine is misfiring and throwing codes.

Really sucks. I did get paperwork and warranty work at a shop that replaced those gaskets and had 3yr warranty. I dropped it off there. I was planning on spending more money there, but found out they are closing doors due to lease not being renewed (land owner sold the property).

I get the car back, thinking all is great.. and everything seems worse.

So now I wanted to put some info out there for me to keep track of these issues. Great work by

SUBARU Engine Oil Leak Causes and Repair

June 10, 2011. Author: 
Described here are the most common causes of SUBARU engine oil leaks.

View the entire photo gallery of SUBARU engine oil leak sources here.

SUBARU Front camshaft oil seals oil leak

SUBARU front camshaft oil sealNote: The front camshaft oil seal leak information applies only to Subaru engines with a timing belt such as the 1.8L EJ18, 2.2L EJ22, 2.5L EJ25.  Does not apply to the H6 EZ30 which uses a timing chain).
The front camshaft seals are behind the camshaft sprockets.  The camshaft sprockets are behind the timing belt cover.  These oil seals can leak with age and mileage, especially the earlier black colored seals.  The later brown colored seals are more resilient.
The smart time to replace the front cam seals is when the timing belt it is changed, since much of the labor involved in replacing these oil seals involves the R&R (removal&reinstallation) of the timing belt.
On the SOHC (single overhead cam) engines, there are two if these front camshaft oil seals.  On DOHC (double overhead cam) engines, there are four of these oil seals.  The front cam seals live behind the camshaft sprockets.  The sprockets must be removed to replace the seals.  The photos below are of the SOHC variety (specifically the EJ22): 

SUBARU Front crankshaft 'crank' seal oil leak

SUBARU front crankshaft oil seal showing oil pumpThe front crankshaft seal is mounted on the oil pump.  The oil pump is turned by the crankshaft.  The front crank oil seal is smart to replace when replacing the timing belt.  Resealing the oil pump is the wise way go since there are other things about the oil pump that can leak, namely the rear rotor case cover screws backing out.

SUBARU Camshaft 'cam' cap o-rings oil leak

SUBARU front crankshaft cam sealThese o-rings are located behind the LH (left-hand) cam cap (on the sohc 2.2L and 2.5L anyway).  This o-ring can get squashed and brittle with time and potentially allow a leak.  The smart time to replace this o-ring is when replacing the timing belt.  To replace it, the camshaft sprocket must be removed.
Also, EJ22 engines have a cam cap at the RH (right-hand) side rear of the engine.  This cap also has an o-ring that can leak oil.  (On SUBARU EJ22T (turbocharged) engines, the turbo oil return goes into this area).

SUBARU Valve cover gaskets oil leak

SUBARU valve cover gasketThese gaskets seal the valves covers against the mating surface cylinder head.  They can shrink or crack with age and then result in an oil leak.  The oil in this area is not under pressure as it is on its way to draining back to the oil pan.
Sometimes the valve cover bolts loosen slightly and can allow oil to leak past the gaskets.  There are also bolt sealing washers that should be replaced if replacing the valve cover gaskets.  A kit is available from Subaru dealers containing the needed valves cover gaskets and bolt hole seals.
If the spark plug tubes on your soob engine penetrate the valve cover (such as on the EJ25 sohc), you should also replace the spark plug tube seals.

SUBARU Spark plug tube seals oil leak

SUBARU spark plug tube gasket sealsSpark plug tube seals Subaru oil leak[/h3] If the spark plug tubes penetrate the valve covers on your soob engine (such as EJ25 sohc phase II), these seals can shrink with time and allow oil to seep past and down into the spark plug tubes.
If you see an excessive amount of oil in the spark plug tubes when replacing the spark plugs, then these spark plug tube seals probably need to be replaced.  If too much oil accumulates in the spark plug tubes, it can result in cylinder misfire from the oil diverting the spark energy. 
Cylinder misfire typically shows up as a flashing CEL (check engine light) (aka MIL - malfunction indicator lamp).  If the codes are read typically P0301, P0302, P0303 and/or P0304 are read.

SUBARU Oil separator plate oil leak

SUBARU metal oil separator plateThis plate is at the rear of the engine.  It provides a hand hole for access during certain engine repair jobs.  Many SUBARU engines came from the factory with a plastic oil separator plate.  These plates can then start to leak with age and mileage.
The solution is an upgraded metal oil separator plate with new screws.  Unfortunately, the engine or transmission must be removed to gain access to replace this plate.  So unless the engine is really gushing oil it may not be practicable to replace the oil separator plate.
However, if the engine or transmission is pulled for some other reason (clutch replacement, head gasket replacement, etc), then it is definitely prudent to replace the separator plate with the upgraded metal version at that time.