Leaving Japan after 10+ years. How much of a pension refund can I get?

As stated, I'm planning to leave Japan. I have worked here constantly for longer than ten years (on this stint).

I'm seeing on Google that there is a ten year "limit;" does this mean that because I've been working for more than ten years straight I can't claim anything back at all? Or can I claim 60 months' worth? If so, will my refund be calculated as my average monthly income over the ten years multiplied by 60?

FWIW I remember I was able to fairly easily claim my pension refund after leaving Japan the first time when I finished my three years on JET.

by ext23