Regarding the other poster's reference to Leipunas, Seiniai, Lithuania.
It's like the location is on the other side of the border in Poland. Seiniai is the Lithuanian place name spelling for Seinai, Poland.
When William (likely recorded as Wincas or Vincas on his ship manifest) left for the U.S., that area was part of the Suwalki/Suvalkija gubernia (Russian for province).
The gubernia was the northern most of 10 provinces/gubernias that comprised the "Kingdom of Poland"/Congress Poland that was headed by the Russian czar.
When Poland and Lithuania regained their indeprendence, the northern half became part of Lithuania and the southern half part of poland. My mother's family were from the northern part of Suvalkija.
Use the www.stevemorse.org
website to search the Ellis Island to find his arrival record (79% of immigrants came through New York). Check off Lithuanian/Polish/Russian for nationality and just use MA or MO for his surname and WIN or VINC for his given name.