Hi There,
The pin housing shouldnt keep turning, but that wont cause your leak provided it's screwed all the way in and the pins in correctly. If there is no damage to your bottle thread, or pin and pin housing it should be just a case of either replacing the oring on the bottle thread, or replace the small yellow oring inside the the pins housing.
If there are any further questions feel free to get in touch again, and if replacing the orings doesn't solve it sending us your marker for a repair is also an option.
Best Regards