So took my IS 350 F sport in yesterday for 10k service and within 10min of giving the car to them the women I was dealing with came up to me and said they found a leak while it was sitting in the garage. So my question is, what could cause the thermostat housing to leak? Rock or freezing? Picture below from invoice...

Not that this was a huge issue, warranty covered it and had a loaner for about 4 hours while they did 10k service and replaced the part.