A plastic/aluminium radiator can easily be cleaned (rodded) out (in fact it's easier and less stress to the radiator itself to do a plastic/ally radiator than a copper/brass one) it involves removing only one tank and should always be the "top" tank (in this case the passenger side) this tank should always be replaced during the procedure as it is the one that cops all the heat stresses and average service life is 8-10 years. Get some prices, as stated above its often more economical to just buy a new replacement theses days.
A coolant "cocktail" can block a radiator in a surprisingly short time, the sediment created will "fall out" of solution starting in the cooler area of the core, you only need approx 10 clear tubes in a core (out of a possible 80 or more) to take all the flow that can be created buy a garden hose (even if it is chased by compressed air !!) so depending on the method of flushing, nothing may have been achieved.
Hope you get this issue sorted, as others have stated once the system is operating as designed you should have no issues, just keep up the cooling system maintenance.....
Zypper

