V...I noticed that you car has a fender mounted mirror..Given the rainstorms we had in the south last week you may have something coming in around the seal there.
I don't know if this idea will be useful on a Spyder, but I have used a flashlight to locate larger openings and places where seals don't fit well. Get in a dark garage and put someone in the car, then have someone shine to light around the seals, gaskets, etc. I know this sometimes works in cases of leaking trunks in cars...Might be worth a try.
Also, you might check the conduit that carries electrics from the engine bay to the dash...Given the rain you had last weeks, anything is possible.
Good luck...