[denisond3]

Just for the heck of it, if you have the cam cover (aka valve cover) off, check that all of the head bolts are still tight. Our family had one that ran for more than a year, slowly losing coolant - because one head bolt (the one in the lower right corner nearest the thermostat housing) had snapped in two.
And when flushing any cooling system, remember that there is always going to be some residual crud in the bottom of the radiator, as well as some in the bottom of the water jacket in the block, and in the bottom of the heater core. Once you have done a typical flush, the coolant may not stay nice and green afterward. It just shouldnt get as mucky as it was before.

I rebuilt the engine in my 91 LX where the machine shop had to mill .006" off the top of the block, in order to get past the rusty low places, down to where it was clean gray iron. This probably happened after a headgasket went bad when the prior owners had it, and they let it sit for many months before getting it fixed.