Elantra issues

[Jane66]

Hi I am new here and don’t know much about cars. My 2005 Hyundai Elantra had its engine ruined after a routine oil change at the shop (was told it wasn’t their fault, this kind of thing just happens sometime, they said). So I dished $2000 to have engine replaced plus radiator, which was said it was not even an original part. So I guess I got cheated at the dealership in the first place. That aside, I have an issue now with the coolant, it keeps evaporating/being used a lot, . I notice a daily film on engine and surrounding area daily and I wipe it off. I literally have to refill the coolant almost every day. I was told the coolant reservoir top cover is at fault and I need to replace it. What do you think? Where can I find this part? So far the only place I found is at a junkyard. I am worried about my car.