Hi Janet, I didn't find anything for David Williams Leath. However if he was an itinerant preacher, I can understand why. If he only preached in Kittitas Co., send me his birth info and I'll search again.
Finding early death records can be a challenge. The state didn't start collecting them until 1907. In my home county, the court house has the early records.
I'd contact the Central Regional Branch Washington State Archives, sos.wa.gov/archives/archives_central.aspx/ . They have many Central Washington county's death info prior to 1907.
After you find his death date, you might be able to locate his obituary if he preached in one town. Successful Searching!