Noisy phone, leaking lights and blinking screen (KX-T7531)

I have three Panasonic KX-T7531 devices which all developed the following problems after 10+ years of operation:

1. Calls are noisy (when listening and when speaking)

2. Various lights are leaking

3. The screen is blinking

I have tried disconnecting each of the components (handset, loudspeaker and screen) separately, but the problems persist.

On the same network I have some KX-T7533 devices (operating for the same number of years) and which did not develop the above problems. These devices seem to have very similar components with a few differences on the main pcb.

I was wondering if it is a single component that is responsible for the problems (e.g. the oscillator) and whether replacing it is possible? Thank you