Water leak driver side, footwell and seatbelt wet

[JL849]

Vehicle is a 2015 Lexus IS 250.  After some heavy rain, noticed seat belt was damp/wet and felt a few drops in the footwell also on the driver side interior.  Interior has a slight musty smell.  Open to any ideas to troubleshoot.  Any guidance on where the drains are that could be clogged and causing a leak?  Could it be the sunroof or windshield seals?  Any advice would be appreciated.

[IS300FSPORT]

Start with checking the rubber seal around the door frame both doors. Then move onto the sunroof looking for a drain hole remove any old grease/leafs/dirt etc.

The clue is on the roof liner once it dries out is there a stain that its coming from the sunroof.

Another option is to get an assitance to stand outside with a water hose on medium pressure & you sit inside the car with a torch listen carefully & look out for a drip with the tap turned on. Depending on how much water has accumulated you may need to lift the carpets up & remove a rubber bung to let the water drain out then use a dehumidifier or hair dryer to dry out as much water as possible. 

[JL849]

Thank you for your guidance.  The rubber seals around the doors look good.  I opened the sunroof (which I rarely use) and cleaned the area out.  Cleaned the two drain holes as much as I could and tested drainage by pouring some water on each side.  One side drained but the other side did not drain at all.  Was able to use some compressed air on the side not draining and it now drains.  My assumption is that during hard rain, the water would collect as it could not be drained fast enough and then started to leak into the interior.  Hopefully that solves the problem.  Now I just have to get the musty smell out of the interior.