It is a mineral based oil. But of very high quality, it is API SM rated, the same rating as the full synthetic genuine oil. Unlikely to cause any excessive wear, but good for bedding in. As for why they added a 5000/3mth service and then dropped it again, remember there was a few issues with the EJ25T on some cars? I would say that was the reason, I've been at Subaru for 8yrs and it was only the H6 that used to get a first service, except for that little stint a couple of years ago.

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F.B. Racing
01 WRX (STI badged)
2010 XR5 Focus
06 Impreza Hatch 2.0i