My sunroof start to leak aii of a sudden when it rains or when I was the car. The driver seat gets soaked. I checked if something is preventing he sunroof from closing properly but could not find anything wrong or so it seems. Is there a simple fix I could do my self?

Camleback sells long (very) flexiable mini bottle brushes that I have found to be very effective. Compressed air is also a good idea.
-Ted
'74 144GL (with sunroof)
'59 PV445

What Flaps said.

Info on the sunroofs drain location is in FAQ. You might try and run a stiff wire down them ... just ensure you have have something blunt on wire end as I'm not sure what the drain tube is made of.

Piercing it would probably be no fun.

I agree, try a wire with a blunt end in the drains.

A second thought, although it sounds like mechanically your roof is fine, I'd doublecheck the condition of your sunroof seals - particularly the front one...
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Jim 90 244DL 243K

..drain holes. the front ones run through the foward body door frame. the rear ones through the aft door frames (i think). get a hose and squirt water down each one and see if they drain or back up. nor sure of the best way to clear a clog, compressed air maybe, or draino :)....good luck

Definitely don't want to use Draino in there.

but compressed air isn't a half bad idea.

Good luck!
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If you listen to the radio in Portland, OR, you may know me as "Portland's Favorite Soul Brother!"