What syatem did water get into?
How did the water get into the system?
Did the repair facility identify how water got in the system or are they guessing?
This is very likely as once the shocks fail and leak fluid, all fluid can and will pass in both directions. It will seep out and will allow water/contamination in. I just checked the TIS(Toyota Information System) and did not see any Service Bulletins pertaining to this concern and there are no Recalls for this.
The best course of action (if you decide to fix it or submit the claim to your insurance) is the try and identify were the water intrusion happened before attempting a full repair. I have never seen this personally other than by an improper repair.
Have you talked to Lexus about this and are they going to cover it?
This is what they will typically do in cases like this. I know of no desigen flaw pertaining to this but as with all vehicle model lines there are pattern failures. This may or may not be a very common one but yet may still persist as an uncommon but heard of one. This could be why the Dealer is trying to get help from Lexus. It is also in their interest to hjelp keep you as a Lexus customer.