why don't you pm our sponsor Phil @ Detailers Domain? He may be able to recommend some products that would help.
Regardless, your seats do look like they have some built up grime on them, I would say you definitely need to do a throrough cleaning of the seats before you put conditioner on them.
I use this to clean my leather and all interior surfaces first, before putting on my conditioner.
(I would apply this and thoroughly wipe down with a MF towel to get all grime off, you might even need a soft bristled brush to really agitate the leather, I say SOFT britstles because the protective layer of the leather is very delicate!)
http://www.detailersdomain.com/1Z-ei...ner_p_106.html
Followed by this to protect and condition:
http://www.detailersdomain.com/1Z-ei...ege_p_500.html
Most of the guys cleaning their cars like to use a one step product for their seats I've noticed, and you just won't get the results you will get from using a dedicated step to a cleaning product, before applying your conditioner. The one step products are too gentle.
Hell, that "bleach mark" might not even be discoloration, it might be the actual color of your seat since maybe his towel had a strong enough cleaner to cut through all the grime!