W124 Broken nipple for expansion tank

I discovered today that the small leak appearing under the car periodically was coming from the hose to the expansion tank. On closer inspection I discovered the nipple at the expansion tank had broken and the hose was loose. Not surprising it was leaking. I have managed to fix a temporary repair by clamping the hose onto the stub of the nipple that is left. I was wondering if anybody had managed to effect a more permanent repair without buying a replacement expansion tank. I was thinking of a metal nipple of some sort but how does one tighten the nut on the inside of the expansion tank?

I am not in any hurry as I shall not be using it over Christmas but it would be nice to sort it out.