Omega B – FL- rust on the front longitudinal support left

hello, I guess I’m about to have to say goodbye to my omega…at the front left side of the long haul, right on the axis, rusts it through! the car was just on the stage to weld, but the workshop refused to do it then, because this place would not be to be welded. unless he had a prefabricated repair plate (3mm). now I ask you, is there such a rep sheet for the omega b? or can you weld there? many thanks and greetings