How reliable are auto part store tests?

I pulled the starter out and took it to the auto part stores to have it tested. Kragen-failed, Autozone-passed and Pepboys-passed.

How accurate are those tests? Should I just put the starter back and see if it works now or just replace it?

Thanks!

 

if you have a volt meter check the power going to the starter at the wire conection could have a bad wire or conection

 

Thanks for the tip. I went ahead and open it up and found that one contact is pretty worn and the other is still good. I'm going to try and repair it to see if it works. However, during the process, I found a reddish orange rubber gasket on the floor...it's about the size of a dime...any ideas where it goes?