Our first horse had a fairly long main (that was almost to his shoulder) and our current horse has a THICK and WAVY mane... The only product I use, and because of it I've never had to deal with wind knots/tangles or breaking hair, is Healthy Haircare Hair Moisturizer: Hair Moisturizer
I make the product significantly stronger than recommended, but either way works.
This stuff is fabulous and can even be used on the coat. It doesn't attract dust or dirt and isn't slick.
The only thing I've noticed is that it is a bit of a magnet for 'love bugs' here in Florida.