i have had great luck in the past using LX -112 from ladd. i used it for Immunofloureses on one micron sections, and compared the results with ultra thin sections on a sloted grid by using anti IgG fitc gold probes. it was quite nice to be able to see the lable through all the steps.
published a paper doing this some years ago, i'll try and dig up the refence.
john hoffpauir