Polyester filler (e.g. Bondo) can work to fill in some cracks. This is fine most of the time. Neos are still quite tough even when cracked.

Plastic mfgrs sell sheet ABS. You can get thin sheet, cut a patch from it and glue it on with ABS glue. Neos are ABS plastic. This kind of repair is what you want if the strength of the seam has been compromised by cracks. Like I said though, Neos still work well even if cracked.
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Mark