RepairPal Certified shops can diagnose and repair your 1998 Toyota Avalon. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.
Can't say how much the repair will be or IF it will leak as it is .. However if you don't use the "moonroof " often and 'leaking' gets to be a problem, you may consider sealing it up and disabling the power circuit......... Just an option.