Kostmayer worked as a reporter from 1971 to 1972. He served as press secretary to Pennsylvania Attorney General J. Shane Cramer from 1972 to 1973 and deputy press secretary to GovernorMilton Shapp from 1973 to 1976.
Kostmayer won back the seat in a 1982 rematch by 2,300 votes.[4] Kostmayer won re-election in 1984 over David Christian by fewer than 4,000 votes.[5] He then enjoyed victories in 1986 over David Christian again by a much larger margin and in 1988 over PA Republican State Senator Edward Howard and then again in 1990 over Bucks County Clerk of Courts, Audrey Zettick. In 1992, Kostmayer faced State Senator James C. Greenwood, who had been a legislative aide to Kostmayer's first opponent, John Renninger. Greenwood defeated Kostmayer with almost 52% of the vote.[6]