Radiator. If you haven't done it yet, replace the plastic OEM radiator with a dual pass aluminum radiator. The plastics are likely ready to crack if they haven't already. I replaced mine pre-emptively and found the radiator cracked at the hose connection points.

Seeing as how you have access to RE-71RS, i'm assuming that you are not based in the US. If you were, I would recommend this radiator:

https://www.sakebombgarage.com/mr-si...ance-radiator/

Otherwise, pick up a radiator from Koyorad.
Avoid mishimoto - they have poor quality control and it's hit or miss if you get a good one or not.