I am considering just replacing the entire radiator.
I replaced the original radiator as it was definitely clogged, I tried to flush and back flush the heater core at the same time. The replacement used radiator then started not transferring heat as efficiently during the summer and I found the heater core was not putting out too much heat.
My concern is that there was enough of the crud left in the system that it was able to partially clog the replacement radiator and heater core. If I change the radiator again, I run the risk of it clogging again.
If I could cheaply flush the current radiator and heater core, I could see if that takes care of the issue or not. The radiator is a single core and fairly small, I could not find anyone making a multi-core, so I think that I will keep having the issue will a small amount of crud clogging the cheaply designed radiator.
I think that a small amount of crud may have found a pocket in the block and resisted the flushing. When I changed the radiator I tried to flush everything, I went as far as replacing the waterpump during the process.
I would hate to keep replacing the radiator to just catch enough of the crud to clog it.
Incidentally, the radiator effect is so minimal, even with a clogged radiator it could maintain a reasonable temp during the winter and pretty much any time the outside temps were under 90F.