Break Master Cylinder Tandem - Repair

On my 2S 130 the Reservoir on the Break Master Cylinder leaks on the not screwed side.
The Master Cylinder is a tandem Version
At Kelvedon they sell Seal Kits for 0,7, 3/4 and 5/8 but i dont know which Version my Master Cylinder is.
Any ideas?
SJ Sportscars sell a complete Tandem Master Cylinder do you think its a safer way to get an non leaking Cylinder.
Thank you for every input

if not seen already you may want to give a glance at one of the former threads on the topic :

https://lotuselan.net/forums/viewtopic.php?f=42&t=38218

swapping the master cylinder may require more work then initially anticipated, esp. if the ports are not on the same side as the original part.

brake fluid is hydroscopic, and many parts can be affected.
maybe this is why yours is leaking, and cheap insurance, also, the difficulty of changing them

Definitely do not get a replacement master cylinder unless yours shows corrosion in the bore. With regards to the size you need - just measure it. Original is best.

Do they? I can’t see anything except one on an exchange basis

https://www.sjsportscars.com/parts-and-accessories/X050J6040W.htm

Thank you Guys, your Inputs helped me. i ordered now a seal kit and will try to fix it

please let us know if the kit you obtained contains the front (“not screwd” end) reservoir seal, this was rarely the case a few years ago (hence my recourse to stacked o-rings)…

That Girling tandem master cylinder was used on quite a few makes and models other than Elan. Ford Escort Mk1 included. I’m not sure if the bore size is the same on the Elan but could check if someone has the data. The Ford Escort kit has that square section reservoir seal. The kits also used to contain the tilt valve although I’m not sure if that’s the case (you need to remove it before you can extract the piston - requires a large Allen key).

ebay.com/itm/223229177044

As I dont know, I shall ask.
Why not new 2cams please.

Outside of the cylinder bore, the pushrods on the 4 that I have are all corroded. This is where the leaking is.

Pushrod or piston? Rarely is there corrosion on the piston unless of course the cylinder has been left sitting with brake fluid in it and not used. Never store or let a brake component sit with fluid in it and always use rubber grease not brake fluid during assembly.

The rod itself
Maybe its canada
I wonder if some beake fluid leaked past the main seal in the cylinder, and got trapped between the outer seal. This corroded the shaft/pushrod and in turn ate up the main

I now received the Master Cylinder Seal Kit from SJ Sportscars X050J6041Z, and you can see the parts on the attached picture. Actually i dont know if the Kit contains the front (“not screwd” end) reservoir seal. I will try to put the things together in the next days