I checked the original Trittenheim text; it's 'Vechtanus',
not 'Wechtam', wherever the latter German interpretatio came from. If
he used a source, it seems it wasn't Norse.
Finally got hands of a copy of Heyerdahl's "Jakten på Odin". Seems he
has rounded up most of the classical references I found, and then
some. He points to Plutarch's reference, in 'Bioi paralleloi', to one
Oltak, ruler of the 'Dandars' (sic, Dardans? "one of the tribes
living in the coastal ares of the Maeotic Sea"), in Mithridates'
army. He had unusual strength and courage in battle, could counsel in
the most important treaties, and was besides remarkable for his
courtesy. He plotted to kill Lucullus and failed. There is a similar
story in Appian's Mithridatica, where the protagonist's name is
Olkaba. Appian calls this man the ruler of the Colchians. Heyerdahl
surmises, since neither was heard of after Mithridates' suicide 63
BCE, that Oltak and Olkaba might be the historical Odin who fled the
Romans. Myself, I think they end up on the variously related heap og
V&r&Tragna - Vahagn - Vahagn - Valtam - Vegtam etc.