Need help - AF problem with Canon EF 180mm f/2.5L Macro

Just received a Canon EF 180mm f/3.5L Macro from an eBay purchase (save the comments) that appeared cosmetically and optically mint in every way. What I find though is that in AF mode it never locks focus, it appears to hunt back and forth around the correct focus point.
I put it on both my 5D Mark III and 1D Mark IV and get pretty much the exact same behavior.

First question, has anybody experienced this before? Is it possible I am doing something wrong with it. I have never seen this behavior before with any other Canon or Sigma AF lens I've owned so I am currently thinking this copy is broken.

As I asked has anyone had this type of behavior with any lens or specifically the 180mm?
If so do you know what the repair cost might be from Canon?

I probably will have to end up returning it to the seller but want to make sure I consider any potential set up issues I might not have thought of.

All help appreciated.

No one is willing to offer any help?

swldstn wrote in post #14598299
I am currently thinking this copy is broken.

Agreeing with you is the only help I can offer; a lens that hunts but won't lock is likely broken.

I had this issue a while back. Had to get the AF motor replaced. was pretty expensive.

Simpleboy wrote in post #14602175
I had this issue a while back. Had to get the AF motor replaced. was pretty expensive.

How much is "pretty expensive". I had a 70-200mm f/2.8 IS MkI that I dropped and it cost $450

check the auction and make sure the item wasn't marked "as is", or they were unable to test and have it marked as no returns accepted.