Ahh yes this again, so if you see my thread about this matter it seems very similar.
things to note that it could be:
1- Radiator leak
2-Water pump malfunction
3-Valley plate sealant issue.
I'm leaning towards the Valley plate issue as it looks almost identical to mine. To give you an idea mine cost £1650 to get repaired by Lexus Tunbridge wells, took 2 days, but the parts took about 6 weeks to get. It generally affects the Americans rather than us due to their harsher climate but alas we aren't exempt from it now. It is definitely not known to the UK lexus garages as mine hadn't even heard about it before mine. They have to tear the engine from top down to get to the affected area, in the end i had my heat exchanger changed too.
Hope this helps.