What, if any, was his association with 610th TD's?
You mention you have 893d's S-3 Journal. Was he staff or line? Perhaps Assistant Operations Officer? Battalion Liaison Officer?
610th was attached to 4th Infantry Division from 25 January to 10 March and 17 March to 9 May 1945. That covers all but about a week of the remainder of the war in Europe from the first date as well as most of your time frame during which he is "unaccounted for."
Where did he go after being relieved of assignment (PCS) to 893d and temorarily assignment escorting replacements (which was interrupted by the train accident)?
Re the DI's. The manufacturer (the largest were Hilborn-Hamburger, Gemsco and another I don't recall at the moment) polished all brass and silver items to a high luster then applied a clear preservative coating, something akin to lacquer. As long as it remains intact, it prevents dulling and tarnish.
(The marine corps issued open-faced brass buckles for the web belt. One of the first things we had to do was remove that coating - it was called "quartermaster" - by soaking the buckle in something we got from supply that smelled very much like lacquer thinner.)
I should probably pay you for all this. I haven't had such a good work-out in quite a while.