UPDATE
After years of doing nothing, slow thinking, finding schematics etc... I finlly managed to understand why the screen was oversaturated in blue and colors wrong.
A few months ago, I decided I needed to remove the monitor PCB from the cab to try a cap kit before going to more exteeme ways such as rejuvenation or replacement etc...
I managed to find low res schematics of the Sanyo 20-DZC (monitor in a box) in Arcarc Xmission Radarscope schematics.
I also managed to find another monitor PCB and found something weird.
On my PCB in the RGB driver section the IC201 and neighbouring holes were equipped with components while this section was bare on the other one...
IC201 (a TTL 7400 chip) is not even on the Radarscope schematics.
I decided to have my PCB mirror the other one and the schematics and did a full cap kit at the same time...
And voilĂ , when put back in place, the monitor provided nice and vibrant colors for Space Firebird...
After 5 years the game is complete and plays perfectly.
A gret learning experience for me.