I hope that the vet can figure out what's going on! That'd be such a huge bummer, it's amazing what people will do just to sell a horse sometimes, especially when a little honesty can go such a long way. Silver is lucky that he's with you though, and that you're going to do your best to figure out what's causing him such pain and soreness.
It could be possible that the scar is just from an ill-fitting saddle, but hopefully the vet will shed some light on the situation and it's nothing serious.
Forever loved, never forgotten; my beautiful Indie. <3 Hoofprints on my heart.