I recently had my RX 350 in for 100,000 mile service and the techs found a leak in my radiator. They replaced the radiator. A day later after driving it about 10 miles I got a steady engine check light. I parked it an a day later when I started it the engine check light was flashing as well as some others and the engine was running rough. Subsequent inspection by the dealership service dept revealed coolant in cylinder #2.
I cannot understand how this could happen. If coolant is in one cylinder, why would it not be in all of them? How can they flush the coolant out of the cylinders without breaking the engine down and rebuilding it?

If it ran hot at all it could be a diminishing head gasket seal there. Don't drive it with coolant in where the oil is. Just be thankful it's bank 2 on the front of engine. Shouldn't be too bad to get that head off and install a new gasket.

If the gasket fails between the water passage and the #2 cylinder then that's where the coolant will go. Do NOT drive the vehicle, if coolant gets into the crankcase it will wash out the main bearings or you can hydrolock the #2 cylinder, in either case you'll be looking at a new engine. No matter how you go about this it's likely to grow as the repair goes on.

You can choose to simply pull the one head and replace that gasket. I don't like that option as you leave a 100k mile gasket on one head. If you can get away with it though, it would be on a Lexus. At this point though, you probably should get a leakdown test done on all cylinders, at least you'll know if the rear bank is holding compression okay.

Anything difficult to get too now would be the time to get it done - water pump or front cam seals, etc. Make sure whomever does the work is reputable and familiar with Lexus engines.