I have used nothing BUT xylene substitutes for quite a few years and have
had excellent IHC staining results.  In the past I used Hemo De from Fisher,
but that has recently been discontinued and replaced with Citrisolv (another
limonene-based solvent).  I do four changes of xylene-like solvent, 3
minutes each, before moving on to the graded alcohol series.

Jan Shivers
Immunohistochemistry Lab
Univ. of Minnesota Veterinary Diagnostic Medicine