Hi Craig,
Very observant question to presume that the back of the headlights were well sealed to protect the reflectors from being exposed to the atmosphere-- yes the backs were sealed; but incorrectly sealed.
Both metal socket holders, (A13118A/B) were incorrectly soldered to the stainless steel headlight shell, thus forming an incorrect tight seal. LOL.
Also both non-metallic headlight wire plugs were missing, the (2) existing wiring harness wires were incorrectly hard wired to the (2) existing headlight sockets, & these (2) existing wires were very tightly wrapped with old cloth tape & wedged into the soldered socket holders, thus forming a very tight rear seal. LOL.
With all new replacement parts arriving for both single bulb headlight/reflector headlights, (because of having original cowl lights), only (2) new harness wires are required to penetrate the new (3) holed non-metallic plug.
Thinking of soldering a new ground wire to each new bulb socket & allowing the new ground wire to penetrate the new un-used third hole in the new non-metallic plug, (A-14584), & next, assembling & sealing the new wire penetrations with same G.E. silicone sealant mentioned above.
Also to insure a good connection, will apply "Kopr-Seal" paste to the metal wire joints between the new wiring harness wire tips & the new metal wire tips in the part of the new headlight socket that penetrates the new headlight socket holders.
Also, after receiving new headlight sockets & new harness, I am waiting for other headlight parts, (one of which is on back order), prior to continuing with the final headlight assembly.
Hope this helps!