It seems like all PS systems burn the fluid over time (based on its smell), but have you ever felt you really overheated the PS fluid to where you lost boost? I would think Mr. Toyota had this pretty dialed in, unless you're in Saudi Arabia. If you're see-sawing the wheel in a rock field regularly, then you may need additional cooling, too.
Steve H. - KE0KNH
Colo Springs, CO
'78 FJ40, '89 FJ62, '98 4Runner