I went with an AFI product, AFI #33021S, which is a stainless steel frame and a blade proclaimed to be "marine" grade. I found this through Jamestown Distributors, after the other 20" non-marine prescribed replacement blade usually referenced through NAPA is no longer available (at least that I could find).
Any 20" stainless or marine grade framed wiper is going to work, HOWEVER, you will find that you might need to do some manipulation to the end of the wiper arm to secure the new wiper blade. On our 2002 282 Sailfish (not so far removed from yours), this included unbolting some parts and figuring a new way to drill and fit the wiper wash down.
As to the switch, it's a 3 way switch with Off in the middle position. If one wiper remains on, even though you're definitely in the middle position, I'd say you're in need of a new switch. Sounds like a short.