We finally were able to identify the whitish silicone-like material used to waterproof various electrical connections including the output lug on the 200 amp alternator and on the starter.
This material is Dow Corning 737 Neutral Cure Sealant. It is used in aircraft applications as a sealant on plastics, metals, rubbers, glass and painted surfaces. This is the correct material to use when rebuilding or repairing a starter, and is the material originally used during manufacture. It is available from a number of vendors, including Amazon and Ebay.
The following link provides useful information and also sells the product:
https://www.skygeek.com/dow-corning-737-neutral-cure-sealant.html