One problem related to driveshaft has been reported for the 2000 Subaru Outback. The most recently reported issues are listed below.
Purchased car with 78k on it. Prior it driving from colorado to wisconsin, had it looked over. Replaced leaking water pump, timing belt, and leaking fwd drive shaft seal. Within a week of getting to wisconsin, radiator and driver side head gasket found to be leaking. Head gaskets are big on Subaru web sights. Soa recommends a "conditioner" to put in the radiator, but it was not available yet. Parts guy said problem was that owners are not allowing car to warm up in cold environments.