A vibration or shudder may be noted on acceleration. If the transmission torque converter is suspected a revised part is available to correct this concern.
The head gasket has a high failure rate due to cooling system problems. Subaru is aware of the problem and has extended the warranty to 8 years/100k miles on many vehicles.
The front oxygen (air fuel ratio) sensor element may develop a crack, causing the Check Engine Light to illuminate. Subaru has recalled certain models to replace sensors that may fail. The Subaru service program number is WXW-80, this is not a government mandated recall.
Front engine oil leaks can develop from the camshaft seal and the crankshaft front seal . If one or more seals require replacement, it may be wise to consider replacing the timing belt as well. These seals are commonly inspected and replaced as needed as part of a timing belt service.
related to trouble-codes, p-codes-powertrain