Went to the Lionel parts site and found versions of Niagara's here: https://www.lionelsupport.com/...;submitButton=Search
From that, went to the Lionel parts site for the VL Niagara 6005 and found the headlight is Unavailable: https://www.lionelsupport.com/...A5-A42D-0251CA1EA993
Item 5 boiler front with headlight and Item 42, Part 6804960310 both unavailable.
Took a look at the JLC headlight but it doesn't look the same.
So, this looks like a call to Lionel. I feel your pain - got into the hobby in 2014 and have sent 4 new Legacy locomotives back to Lionel for repair (smoke unit failures) - so far, had excellent service from them.