I also had a problem with water entering through the Wallas exhaust when in rough water, and fixed it with VersaChem High Temp RED RTV Silicone, Type 605, PN. 65010, which is rated to 650 degrees F. Available at NAPA.
I disconnected the metal flex tube inside the cabin, and disassembled the thru hull fitting. The thru hull was cleaned, and reassembled with the silicone in place around the opening and in the screw holes. The flex hose was reassembled with silicone on the stub end of the thru hull. I also wiped a thin film of silicone on the outside of the first two inches of the flex hose.
This has worked, and apparently lets water which gets into the Wallas exhaust opening flow back out.