From time to time, some rain seems to come into our unfinished upstairs through a couple of the lovers. Anyone else ever had this problem? Any idea how to combat it?

If you are talking about louvered outside vents, then "yes". The 2 gable vents installed in my house (built in 1986) are made of wood and the louvers are flat boards.

When it rains really hard and the wind blows hard from the right direction, the water is blown up over the louvers and into the attic.

I found that the plastic ones you can buy now have a lip on each of the louvers that prevents the water from going up over them.

I couldn't find a plastic one of the same size, so had to do some "customizing".
Hopefully, you can find a size match at your local home improvement warehouse.