It just hit me today that the name Seleukus, for whom the Seleucid Empire was named, sounds an awful lot like the work Seljuk. This is reinforced, in my mind, by two things. 1) the always contentious relationship between [j] and [y] in European languages, and 2) we already know that the Rum sultanate got its name from the Byzantines calling themselves Rome. It makes sense to think that when these more ancient Oghuz people moved into the region known Seleucid, they may have come to call themselves by that name. I know that their supposed origin is in a guy named Selcuk/Seljuk, but is it possible that this is a later interpretation or idea? It just seems so close both in phonology and geography to be a coincidence. Is there any evidence for any of this or am I way off?
This is unlikely. While Modern English has /ju/, Koine Greek (a period ending roughly 7 centuries before the Seljuks showed up) had transformed the diphthong into /eβ/, and it eventually became /ev/ in Byzantine Greek.