The drainage channel below the windshield in the engine compartment was blocked. As a result, rainwater initially ran unnoticed into the front of the vehicle. In the area of the sliding entrance door, the floor covering became slightly discolored. To locate the fault, I cut out a small square around the discoloration of the floor. (See picture) It turned out that the discoloration of the floor was caused by water ingress from the engine compartment, not from the vehicle interior. The fault was rectified by cleaning the drainage channel. The floor I cut out was closed again with a checker plate and can be checked at any time as an inspection opening. The damage was completely repaired. It is advisable to check the drainage channel regularly.