Late post but always seems a relevant topic.
Purchased 2006 Lib (2.5L) in early 2012, fuel economy was terrible (around 11L/100kms), added all the Subaru additives, did a full service straight away (upper engine clean, etc), started on 95 PULP (Vortex) then 98 V Power (both delived similar results), Big diff in fuel economy came with the switch to Castrol 5w30 magnatec oil (not sure what previously used). Now I consistently do 9.4-9.5L/100km city and around 8.0/100 for hwy.