[Stylo N M]

I'm not familiar with this model, and you say you have replaced every component, but unless I'm wrong, I haven't seen in any of the posts, anything refering to the inspection of the rectifier, or the transformer supplying the power to the circuit board.

Have you checked this, for perhaps heat expansion, where there may be a fine break in the transformer coil when it warms up?

I don't know if this model uses an output sound transformer, but if it does, that may have a similar fault on the windings on temperature change, or green spot in the windings.

Paul.