How do I remove duplicates from a list in python if the item has more than x instances?

For eg if I have

old_list = [1, 2, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 6, 7, 7, 8, 8, 9, 9, 9]

and I want to remove elements with more than (x = 2) 2 instances and make it look like this

new_list = [1, 3, 4, 5, 7, 8]