If your dorades are built like mine, there is an aluminum tube that is cut through the deck inside of the dorade box. This tube is what allows the air to funnel down below. The joint between the deck and the tube is somewhat subject to leaks because Tartan used gel coat to form a seal around the tube and over time, this gel coat cracks due to the different rates of expansion and contraction. Does your dorade have a teak lid that you can remove? If so, open her up and take a chisel and chip off any loose gel coat at this joint, clean well with a solvent, then carefully take some good quality caulk, like 3M 4000, and run a good bead of caulk around it.
Another possiblity is the way Tartan used to shield the top of this tube. They used a flat piece of fiberglass to cover this opening from water dripping down from the cowl vent. It is possible that this cover is mis-aligned and water is dripping directly into the tube. This scenario is not necessarily indicated by water finding it's way above the headline, but scenario #1 does.
The above descriptions are from my 1977, T-37 and may or may not apply to a 1980, T-33 but I hope it helps.