GET THAT SADDLE OFF HIM IF IT IS SITTING ON HIS WITHER.
Saddle pads will make it WORSE. They will simply make the saddle pinch his wither tighter, causing more pain and discomfort. You may be able to HELP the situation using a specially designed riser pad, but you cannot fix saddle fit with saddle pads.
A saddle sittong ON a horses wither WILL hurt the horse, it WILL make them uncomfortable, it WILL cause long term nerve damage.
My horse's back is almost crippled due to an ill-fitting saddle in the past, and it was nowhere near the wither. PLEASE think fo yoru horse in this matter...
If you saddle is worth that much, why don't you sell it for that and buy another one, just as nice, that fits your horse?
You are never going to get your horse performing to his best in an ill fitting saddle. He will be in pain. You can get him chiro'd, vetted, whatever, but while you still use an ill-fitting saddle, the problems won't go away.
I daresay this is a part of, if not the main reason, for Rowdy's head carriage.
Please,please,please, don't ride your horse in an ill-fitting saddle for vanity or money reasons. It is not fair on him to be in pain and possibly crippled like my horse was because you paid a lot for the saddle. You should have checked fit before buying any saddle, let alone an expensive one.