Well as you would expect, I had the same problem. Here's what I did. I took out the old screws along with the press fit metal inserts and threw them out, good riddance! Next I went down (with my truck, no plates on back of car now)to the local hardware box store and purchased some large short sheet metal screws. The size that worked best is number #14 x 3/4 inch in length (sheet metal screws). Just screw them into the recently vacated plastic holes where the metal press-fit sleeves used to be. They bite into the plastic and grip real well. Since it is metal to plastic and the screws are plated, they will take a long time to rust but even rusty they will still never sieze. I got 8 screws (4 spares)for about $3 cdn.
Regards,
John