An overcharging alternator in conjunction with a possible poor earth can cause it to happen quicker as voltage is present in the coolant given its conductive and running through different metals being aluminium, iron & steel pipes. This results in ionic transfer which then causes electrolosys...
Flush out the entire system as best you can & use the LLC from Toyota. Its worth the extra $
Original radiator in mine lasted from 1995-2014 when it started leaking at the bottom tank seam however the insides were extremely clean and has always had the red LLC in it
nothing wrong with Koyorad...