I had the same issue for many years. In tried different saddle shapes, position and height. I went from a more flat sad del to a specialized romin evo which has more of a dip in the middle. A 143 worked well for me for a while but I think it was mainly the shape change. I started to get the chaffing again after several months and lowered my seat post. This helped a lot. I recently went up to a 155 romin evo and it seems to be a good combination for me. I haven't gotten any chaffing and I am more comfortable on the bike. Not saying the romin evo is your answer, but changing shape could help.