Good morning y'all

I have leaky brake line, LH rear on type 208 CLK 430. It seems leak somewhere around gas tank.

Now I start to see red display on dashboard, complaining of my favorite word bremsefluesseigkeit so I fill with bottle, but it is how you say inelegant.

I hate brakes but there is too much traffic for only the gaspedal here.

I look under car and looks like one long thing from the rubber line fitting to the ABS modulator behind front headlight. LOL as kids say.

So I think cut old line around rear seat / foot area, make fitting, put union, and buy premade line with fittings and bend it around to fit.

Does anyone know what size is line? I see some mentions of 3/16 line with M10x1,0 fittings, bubble flare (make with cheap Chinese double-flare tool?). But I see others talking of 6mm and who knows what.

Any advice?

Thanks