Since it appears to be a de-lamination... another repair technique would be to clamp the handle and compress the layer back together, then use a water thin CA adhesive like this, specifically made for stabilizing hairline cracks/splits :
https://www.amazon.com/Stuff-Thin-Instant-Glue-HS-4/dp/B017ODPMEO
It will easily wick down into the seam and bond it back together. Once the glue has set, it can be buffed out to make it blend in with the rest of the surface.
I've used this a number of times on wood handgun grip to arrest hairline cracks.