Ah, the double-edged sword of sunroofs. Fun to have but always the potential for problems. Not that it may matter but do you have a wagon with the double sunroofs or a sedan with a single panel? This may help others who post replys.
Time for some inspection and elimination of potential simple problems before you go to a shop and/or take out the headliner. I have always tried to keep all weather stripping clean and well conditioned on the car. I was informed by a sunroof installer that just a bit of dirt on the weather stripping around the sunroof can wick moisture into the car. Also a small stone may also cause a gap between rubber and glass + rain = wet seats. Every time I wash the car I pay careful attention to the sunroofs (OBW) and wipe them with ArmorAll. I have heard that pure silicone is better than ArmorAll-type products but as with most things I have heard conflicting information (and silicone does not give the shine of other conditioners). Any other opinions out there?
Anyway, also open the roof panel(s) fully and check the tracks and surrounding areas. If possible check the water drain hoses which may clog especially in dusty areas or if you often leave the panel(s) open (which may collect leaves, seeds, etc). These may be blown clear CAREFULLY with low pressure air (compressor or canned air). I emphasize carefully because you don't want to blow apart any hose connections. I found the drain lines for the OBW front roof pannel routed down the front window pillars. Not sure where the others are but a shop manual should show them.
Thanks for you reply. My 99'OB is a wagon with dual sunroofs. I found that when I close the aft sunroof, it moves up to the fully close position and the Fwd sunroof moves down and close. But when I released the switch after the FWD one closed, the AFT one drop down a little bit with some little sound from the driving mechanism too. Is there any brake inside the drive motor or the mechanism?