Shocking re-test results

Image by Nano Banana Pro (Gemini)

Have you ever re-taken a language test after a significant break just to see what your score would be, and if your level has changed? Fun right? I think both students and friends can relate to this one. So, in December, I retook the JLPT (Japanese TOEFL/IELTS/TOIC) that I passed many years ago. I haven't lived in Japan for 15 years but my wife is Japanese and I did a bunch of test practice questions as review over the previous few months to sharpen up those rusty skills. Well, I'm embarassed to say I failed in quite spectacular fashion, except the listening part. How can we effectively maintain our languages when we are no longer in a school or using it on a daily basis? Does anyone have the secret formula?