New headgaskets for JDM engine?

[Stevo F]

I’m having my mechanic replace the tires engine in my 2003 Forester. He ordered and received a 62K miles JDM EJ25 and he should be installing it this week. Should I have him replace the headgaskets before it goes in, or were the headgaskets on the JDM NA motors better than the cheap composite headgaskets used on the USDM engines?

[el_freddo]

Replace them with the MLS units. I can’t remember the part numbers but others will. They’re from the EJ25 STi WRX model. 

You’ll thank yourself for going to that effort later. If you don’t, they’ll end up doing the external coolant leak thing. 

If money is tight, drop it in and run it. Over time you’ll see the leak develop. It won’t damage anything, especially if you regularly check the coolant levels. 

Cheers 

 Bennie

[montana tom]

I always replace them. I have found water in the cylinders.

#642 subaru MLS is the one you want.

https://www.ebay.com/itm/132854879269

[ocei77]

As others have said,, replace them.

Just the EJ22 had composite gaskets.

The early EJ25's had single layer gaskets, they later went to MLS types.

O.

[Numbchux]

On 8/12/2025 at 9:25 PM, ocei77 said:

As others have said,, replace them.

Just the EJ22 had composite gaskets.

The early EJ25's had single layer gaskets, they later went to MLS types.

O.

Correction. All SOHC EJ25s list single layer. All DOHC EJ25s have MLS. At least in the US.

There are several MLS gasket part numbers, they changed through the years.

 

The most common problem number ends in 633, and can be replaced with number 642.

[el_freddo]

14 hours ago, Numbchux said:

All DOHC EJ25s have MLS. At least in the US.

Even on the EJ25D? I thought these were a thick composite gasket which was half the issue with these engines… 

Curious. 

Cheers 

Bennie

[Numbchux]

5 hours ago, el_freddo said:

Even on the EJ25D? I thought these were a thick composite gasket which was half the issue with these engines… 

Curious. 

Cheers 

Bennie

 

Well, it's more complicated than I implied.

The current part number, 11044AA610, is steel as far as I can tell. There are 3 older part numbers that were replaced by the 610, I am much less clear what the material of those were, either from my memory or service manuals. So the factory installed ones might have been a different material.