I've ridden in rain countless times and never had a problem. (Though that's modern boards with ball bearings specifically designed to prevent water ingress; perhaps the 1970's stuff was more vulnerable?)
Skating in the rain is great, everyone should try it!
Actual branded skateboard bearings today are deliberately nerfed to allow the elements in, it sells more bearings. At least that's the case with all the ones they sell at the local skate shop here in Berkeley... one side has had the seal completely removed, the balls and cage are exposed. They rust very quickly ridden in the wet.
Skating in the rain is great, everyone should try it!