How to season / care for a Bundt pan?

Bundt pans (and cake pans in general) are not normally seasoned in any way.

Instead, they are greased and floured each time you make a cake. The traditional method is to apply butter or oil to the interior (the easiest way is melted butter and a pastry brush, but you can also use wax paper or even clean fingers to apply solid butter).

Then you flour it by putting several tablespoons of flour inside the bundt pan, turning and shaking until it is well floured, then shaking out the excess.

Oil or solid vegetable shortening may be substituted for the butter.

In my experience, 99% of the time, using a simple spray oil will do the job just as well, with much less fuss and mess.

I just bought one at a garage sale that was a Nordic Ware heavy cast aluminum still in the original box. It is a non Teflon coated original. The box states to use non salted shortening like Crisco, generously applied, and temper in a 200-300°C (390-570°F) oven for about an hour.

I inherited my mother-in-law's cast aluminum Bundt pan several years ago, the one we had given her as soon as they came onto the market back in the '60's. It had been well seasoned over the years by the many, many perfect pound cakes she had baked in this pan.
I feel certain that she only washed out the pan with water, no detergent, after each use, and wiped it dry with a paper towel. She used Baker's Joy with flour before each use, and the pan baked the most gorgeous dark exterior on the cakes.

My pan, on the other hand, only a few years less old than hers, does not turn out a cake with a nice crust. I'm sure now that it is because I've always washed it with dish detergent after each use.
I am reseasoning my pan today and will not use detergent on it, hoping my pan will become as well seasoned as hers.