Those rain channels at the foot of the rear window always get in a bad way Pascal,the small tubes get blocked aswell, mine were equally as bad as yours.
I did a 100% strip of my frames,glass out, new rubbers.
The frames particulary on the front windows spring apart,maybe worse on a split as no quarter lights(vent windows)it's a big headache getting them back together.
I had to use two big wood working clamps and wind them in.All the time the new rubber is moving.Not a job i ever look forward to doing again.
But i really felt like i had achieved something when they were back complete again.