I bought my '01 off eBay for a project for my son to drive. Low-budget so not a "replace everything and start over" exercise. He doesn't get his license until September.
It had brown mud in the radiator and a clogged heater core.
After numerous flushes both ways, the heater core unclogged but would eventually re-clog.
I made a filter for the inlet heater hose using a remote oil filter mount and an oil filter.
After pretty much monthly flushes, it has settled down.

 

I am sure mine will need a good flush or 4