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It could possibly be hydrolic fluid coming from your
convertible top motor.The convertible top motors are
known to fail sometimes or leak.
Where is the leaking coming from??
I have a 98 also. Mine is coming in through the bottom corners of the rear window. You can put some black window silicone to "glue" the window back together for a temp fix. But eventually (which I need to do) is just have a whole new top put on.
Or just let it go, and it seems to drain somewhere. Just let it air out every so often.