He was post legged in the rear but if he served you well then its not an issue. I will take a good temeprment over some conformational issues any day. He lived a long life and you have good memories so in essence he was perfect.
I am thinking about writing a book on conformation (a tutorial guide) and I would like to use your late horse in explanation of the conformational fault "Post legged". He will not be used in a negative manner what so ever. Its mearly for teaching purposes. You don't have to, its your choice.
"The question is not, can they reason? nor, can they talk? but, can they suffer?" Jeremy Bentham