That is good news that the old radiator was clean in side. Coolant is so much better now. The reason I say to replace proactively is I have had a few 10 year old plastic tank radiators fail in violent fashion. One time the tank cracked and leaked everything out in 30 seconds. Another time the input broke completely off where the hose clamps on. Cooling failures are no fun as they can leave you on the side of the road or worst case, ruin your engine.

 

Yes that happened on old Mercedes.