You can steam iron (on low heat, using a towel between the iron and the garment) Gore-tex and most waterproof breathable fabrics. Generally this is supposed to "refresh" the DWR (durable water repellent) coating.
Nik-Wax makes a special detergent for washing waterproof breathable fabrics. The also make both a spray-on and wash-in DWR that will help water bead up on the fabrics. In my experience this stuff wears off fairly quickly. These products are available from REI, EMS, and lots of other outdoor shops.
If your drytop is leaking through the seams you can buy seam sealer and take care of that easily. If you wanted to go the extreme route you could just paint the entire inside of your dry-top with the seam sealer. It wouldn't be breathable anymore, but it should be totally waterproof, just you and your sweat inside.
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