I use the "gel" type superglue to stick my models to the base if its already been completed, it gives a much better grip than the normal liquid types. so much so that if the model comes off the base it normally takes the sand with it.
Yeah that's pretty much how i've fixed it this time round. Pulled the legs back off and the sand came with it. Scraped a bit more off the base with a modeling tool, then superglued as normal. Having sprayed them as well, the paint does seem to have fixed the sand in place more. Almost painting time!