Can you please check the rubber seals around the door aperture?
Any damage to the seals may point to a replacement being required.
If you find nothing here can you remove the rear passenger door panel and check the sealing of the door membrane?
If you run water down the outside of the rear passenger window does the water drain out of the drain holes at the bottom of the door or is it seeping in around the bottom of the interior door panel?
Check the drain holes at the bottom of the door are clear.
If seeping in around the door panel you will need to remove the panel and check the membrane.
The membrane should be completely sealed all the way around with sticky butyl rubber adhesive. If you have a leaking membrane it will cause the problem you are experiencing.
Tuesday, February 11th, 2020 AT 9:18 AM