93 CV new but old problem

I have a 93 ford crown vic 4.6. The starter went out in Dec. last year (12/06) We replaced it. At 1st we replaced it with a "refurbished" starter and that lasted about a week, then we upgraded to the best auto zone has, Duralast Gold or something. Now since then I have had to go back and get replacement for it at least 3 times. Just put on a new one
Tuesday (08/07/07), and 1 time yesterday and 1 time today i had to climb under the car and tap it with a wrentch. I'm starting to think its not just the starter.

What should I do next?

Im about to roll the thing off a cliff and see if it "starts" then.