I always season the new stuff. If you don't strip it, then I suggest you do my method outside on a gas burner. I never season cast iron in the oven. I'm positive that isn't what my grandparents did...nor the generations before them.
I gently heat the pan until hot, then crank the heat until it is as hot as you think it can get. Then I drop a heaping spoon of lard or bacon grease in the pan and swirl it around. You want to quickly coat the bottom while it is still scorching hot. Then tilt the pan at a high angle and coat as much of the sides as you can without spilling any oil. Dump the oil and swab out the excess with a ball of paper towels. Then wipe it out again with another couple paper towels...this time coat the outside & bottom with the moist towels. Let it cool and put it away. It will season further as you cook.
