Irishman

Check under the plastic tray nearest the rear bumper for water in the corners. Very common issue that can cause serious problems if left unchecked.

Because you had condensation you should check in the boot under the black plastic tray nearest the bumper (two plastic pins hold it in place) for signs of water ingress in each corner. It's a common issue that can cause serious problems if left unchecked.

Lock the car using the key at the drivers door, remove key wait a few seconds then open the car with the key, leave the key in the lock for a couple of seconds then turn it again to open the already open car. Your rear door should now be working.

I recently changed the 12v battery in my 2007 RX400 and the rear door would not open from the internal button or manually. It was a very quick simple fix to reset it. Lock the car at the drivers door using the key, remove the key from the lock for a few seconds. Open the car with the key at the drivers door, leave the key in the lock and a couple of seconds later turn the key to again open (the already open) the car. The rear door can now be opened manually and once closed will also work from the internal button.

I had similar issue with my windows and rear door in my 2007 model last week as well and it was a very easy fix. For the windows, go to the individual window control and open the window all the way down and then close it and keep the button held in the up position for a couple of extra seconds. It should then work from the drivers door controls. For the rear door, lock the car using the actual key in the drivers door lock. Remove key for a couple of seconds then open car again with the key. Leave key in the lock and again turn it to open the car (which is already open), you can now open the rear door by hand and when you close it you will be able to open it from interior button as well. Hope this helps, it scares me when something goes wrong with my Lexus as I automatically think its going to cost thousands to fix. Then when I find the usually very simple fix it restores my faith and confidence and I give the old girl a good clean inside and outside and appreciate the style and comfort even more.