First, check the wires themselves closely -- they may be pinched or parted. This can easily happen when the hot shoe's "roll bar" is installed.
If the cells need to be replaced, in all likelihood you can simply exchange eyepiece/cell assemblies with a "donor" part from a "dead" body -- impact, liquid, etc. Olympus' quality control was such that response from cell to cell is almost identical, so chances are no significant adjustment will be necessary, so long as you find cells with identical color wires -- and I believe there was only one "type" of cell used in the "N" models.
If you do need to remove an individual cell, just carefully pull the wires out of the glue holding them in place, cut through the glue holding the clear slide over the cell with a small blade, then gently pry the cell out of it's well -- it's held in place with a small dab of contact cement.