I have made some enquiries about a fix for mine (Gen V) and it seems there are about 6 options:
1. Live with it and keep on lubing.
2. Pay $ubaru for a new pair @$600 each
which will have the same probs later on...
3. Pull you front struts out, send them to Sydney to get rebuilt with better seals that won't knock. 2 weeks is my guess....
4. Get some coilovers, but good ones even more exxy and may have legality issues in some states. Can be harsh riding. Cheap ones available but quality suspect.
5. Replace with KYBs or Sachs from the USA or U.K. which they have available for the Legacy there but are not officially offered in Oz. These may be too soft? But they claim to be OE replacement. They are relatively cheap online in the U.K. For about £60-80 each plus delivery.
6. Replace with cheap KYBs to suit the stock model from the USA or U.K, pull the guts out of them and fit adjustable Koni inserts that are made for WRX to get equivalent ride/handling as the original Billies.
Haven't looked at Monroe but they are cheaper still, not sue if they make one to suit anyway.
I like option 6 the best, it's what some the lads in the USA are doing on LegacyGT.com.