I must be missing some previous entries on this thread - the first I see was sent today at 4:56 - but are you saying the SD card will not STAY IN the card slot ON THE CAMERA? I don't know if this applies to the Advanced version of the P3, but on the Standard version the end of the SD card will be just barely below the outer surface of the camera body when it is fully seated - maybe 3/16th of an inch or so. If it goes in that far, you might try putting it in and then holding it in place with a piece of tape, then see if you can record onto the SD card.
If you send it back to DJI for repairs it is going to cost you the price of a new gimbal. DJI does not repair or refurbish anything you send them and then send you back your drone. They just grab a like item off their supply shelf, install it, give it a quick test, then bill you for the part itself, plus a labor charge (and don't you, like me, wish you earned something around $65.00 /hour to work on drones?)