Why didn't Al Molinaro play Murray?

As was stated in the other topic, they didn't bring back all the original actors, which wasn't too much of a problem, I guess — except for the Murray character, who was really even more important than Myrna (IMO). They brought back Penny Marshall to play Myrna all right, but Al Molinaro was omitted. Why wasn't he there to reprise the role of Murray? Was it money? Did he hate the script? Does anyone know?