Tranny slipping…

Okay, I've been enjoying my beautiful machine on small trips finally. There is always SOMETHING to look after, isn't there. Anyway, she slips fairly significantly from 1st to 2nd gears. Presuming she's healthy (only 24k original miles) what could be the culprit? Fluid? I'll check it again. Do I need to adjust the bands? Any ideas? Thanks.
Author: 69 Polara