Radiator question

Ok, so over the weekend on my 03 330ci I replaced water pump, thermostat, upper and lower rad hoses, expansion tank, converted to hydraulic tensioner, swapped the water pump pulley for an aluminum one, as well as the mechanical-electric fan swap. It all went great, couldn't have asked for an easier time. However, when I had everything off I noticed that in the little elbows where the rad hoses connect to the radiator itself, there was a lot of crud in there. It was easily scraped off with a screwdriver, but for the most part I left it alone. There was nothing in the old expansion tank, nothing in the old rad hoses, nothing on the old water pump or in the block cavity, and nothing caked in the old thermostat. I haven't owned this car long, so I made sure to do all of this to make sure everything was up to snuff. I noticed when draining it, the coolant was green, like you would get at autozone or wallmart :thumbdwn:, not blue like it needs to be. I'm wondering, :loco: is this stuff is additives from improper cooling, or maybe mineral deposits from bad water, what do you guys think? I couldn't get any pics unfortunately, but it looked a lot like when hard water with a lot of minerals leaves a grime around a water faucet, or something like that. But with the green coolant I'm not sure. I Made sure to put blue coolant back in, and have checked a few times since and haven't noticed any grime floating around in the tank. My worst fear is that the prior owner had a leaking radiator and poured a bottle of stop leak in it :thumbdwn: I hate when people do that. And if that turns out to be the case, I will be replacing it entirely pretty soon. I guess my questions are, A) what do you think this stuff was? And B) do I need to start looking at replacing the radiator preventatively? And if so, how soon? Thanks a bunch guys. Y'all take care.