Hello and thank you for using just answer!
No I would NOT replace the entire headlamp here.
Switch the driver and passenger side bulbs here (careful not to touch them).
If the problem stays on this one side then the issue you have is the headlamp ECU that is inside the headlamp and this can be replaced seperately.
ok, what sucks here is While the headlamp ECU is a seperate part it does not show this as available to purchase seperately now......they make you purchase the entire headlamp, they initially offered all parts of these lamps seperately when this car was first released to keep warranty costs down, looks like they have changed this now that the car is 5 years old.
I can tell you that the headlamp ecu that you linked me to on ebay is a SCAM, if you look closely at the pictures you will see that while it appears to be 2 different angles of the same part this is actually 2 different parts.....neither of which are good part #'s in the Lexus parts database I am looking at here. (I have access to the FACTORY parts catalog)
What I would recommend here if you want to keep costs down is to purchase a used headlamp assembly that you can pull the ecu out of rather then installing a questionable one.
I would still swap the 2 bulbs as I originally stated to be sure this is not a bulb issue.