you are right about the iron... low iron is an easy bruise. ... I will tell you that when i use a preacher chair, if my arms aren't positioned correctly and my arms don't hang low enough on the chair, the pad would rub or i would have my triceps laying on the pad and it would cause a bruise...
i know you've been on here forever, so don't be offended when i ask this, because it seems very newbie, but is the seat high enough so your arms are completely over the pad? sounds dumb, but raising the seat a little higher got rid of bruising for me... and i never get bruises from anything else.