F4 dc offset problem

Hello everybody , i have a problem with my f4 amplifier.My right chanel the dc offset when i turn on i have -70mv and after 3 hours is near 0mv , but with my left chanel i have some problems when i turn on everytime i have different value and and goes up and down very fast and the las value was from 86mv to 120mv in 10 minutes.

Thx for help, greetings from Romania.