I've only done a few, so I'm no expert by any stretch.  I haven't gone to any great
lengths with these and so far (knock wood) they've turned out ok.  I have them fix
for 48 hours in 4% formaldehyde at room temp.  Then I process them using the
following schedule:

70% reagent alcohol - hold until processing begins, usually 3-4 hours
ProSoft (Anatech)x 4 stations - 1:00 each
ProSoft - 1:30
ProPar or ClearRite3 xylene substitute x 3 stations - 1:30 each
Paraffin x 4 stations - 1:00 each

I use pressure/vacuum only in the paraffin stations, and do not use heat in any of
the other processing stations.  Although the times seem to be extended, the
solutions I use tend to be gentler to the tissues than regular alcohol and xylene.

Since you're doing immunohistochemistry on these, I don't know what deleterious
effect extended formaldehyde fixation will have.  As previously suggested, Davidsons
may work (though any mention of acetic acid in fixative to the researchers here
usually makes them flinch).  However I would shorten fixation time considerably
using it.

Teri Johnson
Managing Director Histology Core Facility
Stowers Institute for Medical Research
1000 E. 50th St.
Kansas City, Missouri  64110
tjj@stowers-institute.org