So, a mistake on my part. The model E and later apparently come apart reasonably easily and can be cleaned that way. However, the earlier models are riveted and require more finesse. Assuming everything is intact and just in need of cleaning, a plastic pry tool can be used to remove the metal “keepers” from the translucent eye-pieces. Once the unit can be blown out and the actual lenses cleaned with a long cotton swab and alcohol. The translucent portions can also be cleaned up and then re-installed.