I am quite sure this is the traffo since when I swiped the traffo from the other speaker there was no short.
I measured AC and impedance on the good speaker :
Primary - Blue-Black: 108Ohms, 240V (AC)
Secondary - Yellow - Green: 2 Ohms, 18 V (AC). for some reason both yellows gave me 18V with the green, I was expecting one to be -18V, maybe I missed something.
The bad traffo measures same impedance on secondary, but 18 Ohms on primary (10X less).
So it seems there's a short in some windings of the Primary.
I have a local service that rewinds those transformers for 30€ to 45€, so I would resort to that.
i don't know if you have a transformer rewind service where you live