I have Marantz tuner &

Question

I have Marantz tuner & preamp AC500 conected to 5 amplifiers and speakers in 13 rooms. System was working great for 12 years. Now, I have to reduce the volume on Marantz preamp, from 12 to 9 to avoid amplifiers clicking (going to prevent mode). Am I correct that preamp output changed for some reason so that I can't play as loud as before?? Do preamp deritoriate with time?? What should I do??