Hyro units usually run on multi grade oil, if the oil has not leaked out on the garage floor it will most likly still have enough, heat is the biggest killer, check the brake is not binding, if it has a resivoir, check the oil level here, as the machine heats up the oil gets a little thinier, if there is any scaring on the internal centre section it will get slower and slower until it stops, i think you have a problem like this, it would need to come apart and see how much damage has been done, this can be a very expensive rebuild with the cost of new parts.
Husqvarna man
April 2010