starting issue

Are you saying the gear throws out and engages the flexplate but wont turn it? but after many tries it turns it and the engine starts ? Those have a starter solenoid mounted on the starter and a starter relay up the positive cable above, right? Sounds like power gets there, volts are available to operate the pull in winding, but what about the hold in winding? Then when the gear throws out, it intermittently makes good contact to run the starter? but the voltage drops? or it does not make good contact ? The thing is, the bench test being good with booster cables, you are not using power and ground from the block an the posi. cable. I would run voltage drop tests, then if good, remove the new part's attaching bolts, ground it. then try. loose solenoid, connection surface area, and the way the part was assembled can all still be factors. Each part can have differences and the cable's ability to deliver can be compromised, the ground can be an issue, or the make of the parts in use can fit oddly. This one will be a teacher for you, or your technician. Even a starter drive can be oddly made and used on a remanufactured part, and the swing lever could be worn on both starters. see what you are getting power, volts, amp draw, tap on it. That's how I fixed my last starter issue. made one good one out of 3. imagine that?