Quoting Andrew Ramage on his request:
"David Macklin has reportedly passed away. His former manager and I are friends - she (the manager) and David were extremely close, although David lived in New Mexico and she in California.
"The IMDb can lag on info and there are lots of errors on there. It has his birthdate as 1946 when he was born in 1941 (he graduated high school in '59 and came to Hollywood the next year I think - "The Apartment" (1960) with Jack Lemmon and Shirley Maclaine was one of his first roles...he was at least 18 then, definitely not 14, as he would've been if born in '46.) I am in touch with his old manager, Donna, who has absolutely confirmed that he died; she posted something on Facebook about David's final hours and that he died peacefully (don't quote me on this sentence though). If it didn't happen and he's still living, I would be very shocked."