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!

I skated in the 80's and as I remember skating in the rain was pretty hard on the bearings. I would keep a beat up older board as a rain board.

Power slides were so much fun in the rain.

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.

Boards were fine. As another person commented it's the wheels' bearings that didn't like water that that much. But these were easy to change once in a while.