[DaJo]

I normally wait at least 3-5 mins (depends if I'm late) from cold start before driving up to operational temperature. I also don't race the engine over 2.5K RPM... After about 10 minutes of light-foot driving, I usually rev up to about 3K-4K range.

My guess is that maybe the oil isn't thin enough to enter the oil passages to properly lubricate the cams when not in the temperature range. It could be a slight design flaw on Subaru's part.

I don't know if this helps or if it's the reason, but just throwing my 2 cents out there.