Russ,

He does not embed in PMMA, correct, just grinding specimen?  to get the 
grit out, try a very gentle ultrasound in buffer, this will release the
gunk, and you could put some Tween 20 in the buffer as a detergent, then the
sample is cleaned and ready for ICC, sort of a equilibration to buffer being
used.  

One thing that may help, gluteraldehyde is not the best fixative for
ICC, paraformaldehyde or even NBF may be better.  Glut is such a tough
tight crosslinker.  As thick as his sections are, he may need to so some
extensive time blocks, and stains.  What were the thickness of his 
sections, I have seen brain sections 30 um thick, people probably do 
thicker for ICC, vibratomed, and used detergents, plus longer times for
everything.  Sounds like a similar scenario, and not easy. 

If his specimens are embedded in PMMA, Neil Hand is the ICC guru.  

Gayle Callis