I'm no expert, but here's what my grandma would tell you ...
- carefully clean off anything 'loose' re your old sealer with a soft brush
- apply new oil based wood primer over any areas that the old sealer has flaked off
- spray a new layer of oil based wood primer over the top of the existing sealer and touch-up primer
- spray two coats of oil-based exterior / interior semi-gloss paint
According to grandma, a unique problem with wicker furniture is the extreme porosity of the 'wood'. Thus it's essential that a complete layer of sealing primer is in place, or the wicker will soak up paint like a sponge.
The second unique problem with wicker furniture is flexing every time it it 'used'. Regular latex paints cannot handle the flexing as well as oil-based, thus will have a tendency to crack and flake off. However, since grandma's days, 100% acrylic paints have become available that, in theory, may be able to handle the increased amount of flexing as well as oil-based.
PS for the same reason of flexing, it's best to not move or 'use' repainted wicker furniture for several days so that the new paint will have the opportunity to completely 'cure'.