Check this out.. they leak in a couple places, all explained here.
1) The seal between the plastic outer frame and the roof - this almost always leaks 100% of the time, it was a little adhesive strip that decays by now - 20+ years later
2) The rubber seal (replaceable with a Brit-Part seal), between the glass and the plastic frame - PN EEQ500010. Be sure you put it in the right way, it's actually easy to install backwards.
3) At the drain tube trays, where the ends either break off, OR the plastic trays leak between the metal main sunroof bottom panel and the plastic of the drain tray.
Also:
-- Check that your drain tubes (in the rear sunroof) aren't routed "uphill" from the sunroofs, both of mine were from the factory. Literally how is water supposed to flow uphill ha. Mine leaked whenever in my driveway I parked with the nose up, which it's always nose up. Rerouted them with slight downhill slope and some tiptoes on the little wire harness holders between alpine windows and rear side windows... and much better.
-- Everyone recommends starting to seal up every last hole, screw and mounting point on the lower metal tray. You don't need to do this if everything else works and you have a good rubber seal between the roof frame and the glass (#2 above). On my truck, after I replaced the sunroof seal on the rear sunroof, I hadn't reattached my drain tubes, and NO water gets in between the glass and frame into the drain trays anymore. I believe that the drain tubes are really meant for overflow, or if water gets thru the seal -- not regular drainage. The idea is to keep water out of the sunroof with the new seal.