"Mr. Sliker revealed a resonant voice of good range and power, well in focus most of the time, smoothly and expressively handled, and with sufficient agility to negotiate the florid passages of the baroque music he performed. He made it evident that he is a performer with imagination, who understood quite well what the music on his program was about, and showed considerable skill in communicating it to his audience."
In 1959 Sliker joined the roster of singers at the New York City Opera where he appeared in a number of comprimario roles through 1961. He notably portrayed one of the Seven Deadly Sins in the world premiere of Hugo Weisgall's Six Characters in Search of an Author on April 26, 1959 and sang in the 1959 production and cast recording of Douglas Moore's The Ballad of Baby Doe with Beverly Sills in the title role. In 1960 Sliker was a soloist in a performance of Wolfgang Amadeus Mozart's Litaniae de venerabili altaris sacramento with the Boston Symphony Orchestra under conductor Hugh Ross at the Tanglewood Music Festival. In 1961 Sliker was invited by Rudolf Bing to join the roster of singers at the Metropolitan Opera. He made his debut with the company on November 29, 1961 as one of the noblemen in Richard Wagner'sLohengrin with Sándor Kónya in the title role, Ingrid Bjoner as Elsa, Margaret Harshaw as Ortrud, Randolph Symonette as Telramund, Jerome Hines as King Heinrich, and Joseph Rosenstock conducting. He appeared annually at the Met through 1989 in a large number of character roles, including Ambrogio in The Barber of Seville, a Croupier in Manon, Forester in Don Carlo, the Gardener in La traviata, the Guard in Rigoletto, Handsome in La Fanciulla del West, Jankel in Arabella, a Lackey in Der Rosenkavalier, the Sergeant in La Bohème, the Steersman in La Gioconda, and a Villager in Pagliacci. On September 16, 1966 he appeared as the Sentinel in the world premiere of Samuel Barber's Antony and Cleopatra for the opening of the new Metropolitan Opera House with Leontyne Price as Cleopatra and Justino Díaz as Anthony. On March 18, 1977 he sang the role of the Physician in the Met's first staging of Alban Berg's Lulu with Carole Farley in the title role. His final and 509th Met appearance was as Guccio in Puccini's Gianni Schicchi on December 16, 1989 with Bruno Pola in the title role, Hei-Kyung Hong as Lauretta, and James Levine conducting.
Later life
Sliker lived in retirement in Helena, Montana at the Waterford retirement community. His last public performance was in Helena during the mid-1990s when he performed for a benefit concert at the Myrna Loy Center for the Performing and Media Arts. He died at the age of 86 in Helena and is buried at the Lower Valley Union Cemetery in Califon, New Jersey.