Well I found out that I'm pretty sure the guy has used just water in the cooling system. Am I screwed with this? I popped the cap to see what the color of the fluid was and it was clear. Reached my finger in and wiped the inside neck and there was black crap on my finger. Should I take this to get it professionally flushed? Or would I be able to use a garden hose to push the old out along with the nasty deposits then top off with any old brand 50/50?