just skimmed after the first few posts, call me lazy, but don't bother with flushing the core or anything. the coolant on the ground is coming out of the hvac enclosure, so that it will not fill the cab instantly. buy a new core, and replace it. sometimes, you can find a crack where the fitting comes out of the core body, or somewhere accessable, and simply solder it back together, but, being a 98, chances are that it leaks because it rotted, at which point, even if you could solder it, it would just soon fail again.