The reflector is designed to work with an incandescent bulb and will not work right with LED. On top of that most replacement LED bulbs i came across are pretty poor for this application and will most likely be worst than stock.
I would either change the whole assembly to a specific LED one, or do what i did, which is just to buy a good quality replacement bulb.
I used a Philips vision plus, and it is a lot brighter than the stock japanese bulb.