Micelis, As James said you need to find out where the fluid went - I had exactly the same problem, in the end I had to have the pump reconditoned as this is a common problem with the LS400.
As you look at the pump from under the bonnet, about 2" to the right there is a small "stem" that sticks up, if you get a piece of tissue, "twist it" and feel around the top of the stem, if it is wet your pump needs fixing (it is very difficult to spot with the eye) - Also check the tray at the bottom of the engine behind the rad - this is a common place where the fluid runs after goin through you alternator.
If you ignore this (like I did

) it will ruin your alternator as well, total cost to me to fix both was £800 - If you catch it in time and just have the pump reconditioned it will cost you about £200
http://www.powersteeringservices.co.uk/ did mine for me - (a new pump is £390 + VAT).
Don't make the same mistake as me - you will kick yourself, it may seem like a small problem but it can become very costly