Clutch master cylinder with two plugholes

[Atmobil]

So I went off and ordered a new master and slave cylinder for my D100 from rockauto as rebuilding the ones I have is outside of my knowledge-level and there is no shops here that have that service anymore (we are a nation of replacers)
rockauto do say that the clutch master they have listed is for a Town panel or Town wagon but the technical specs looked to be the same and at 35,79$ I thought that I better get one.
What I did notice (and that was some time after it had arrived) that it had two plug holes in it, one in the end/front and one on the underside:


I did install it today and after completion, I did have a leak from the bottom hole. So, had anyone here done this before. I was thinking I could get a plug to seal the hole with. If I can, anyone know what a plug like that is called and maybe what it looks like?
Is there a place to order one?
There may be some shops around here that might have something like that but as we are a semi-comunist country most stores that have such things close at 16.00 in the afternoon (so I have to take time off work to go on the hunt for this thing that I don't even know exist)

The old one:


Does the town panel/wagon have two lines out of the clucthcylinder? If so, why?

[my5thmopar]

Same threads as the one that the line is connected to. Just get a plug for the bottom. Do you have hardware stores? They will have it. Someone will chime in with the thread size. Craig Of course I just realized its metric there.

[Atmobil]

Yes, I'm thinking that a plug with the same threads will work but how to get one. I have a couple of stores that I can go to and ask but as usual I will have to do it during my working hours as they are only open monday to friday 08-16

[BigJimG]

Any auto parts store that carries brake line fittings should have it. I have seen it listed as a "Brake Line Plug". I used one to plug the distribution block line going to the rear brakes when I converted to a dual master cylinder.

[Wildergarten]

Same threads as the one that the line is connected to. Just get a plug for the bottom. Do you have hardware stores? They will have it. Someone will chime in with the thread size. Craig Of course I just realized its metric there.

If I recall correctly, that is a 1/4 NPT thread. Use teflon tape and you should be OK. HOWEVER, looks from the photo like it might be your inverted flare that is leaking. Those do crack upon occasion. So I would pull it off and take a very close look, perhaps with a magnifying glass and a mirror. If it is cracked, I'd replace the whole line.
M