Agreed that Nissins is the best way to go easily .
BEHR is OEM -but- they also use that damn bio degradable German plastic crap that causes the upper hose nipple to detach without warning for no apparent reason
.
I was lucky when this happened on my '82 240D ~ I was in town and it left *barely* enough of a stup that I could re attach the hose to it and carefully motor on home .
I got a brass Chinese radiator at a junkyard and had a custom core installed, so far so good but it was a bit of a PIA and I don't see many W123's in the yards like I used to ten years ago .
If your current radiator isn't leaking or broken, cleaning it with the citric acid and water mix really works well and brings the entire cooling system up to snuff at the same time .
It takes a fair bit of time & effort to do it properly on the average well clogged cooling system but you'll love driving in Death Valley with the AC going and the temperature gauge not exceeding 85* C.....