My plastic reservoir on my stock master cylinder was toast. Initially I was simply going to go with a new replacement but the originals are no longer available. You can get a new stock Triumph part that uses .7” bores for both front and back braking circuits. The S2 Europa has .7” for the front and .65” for the rear. Having .65” for the rear slightly increases braking force in the back relative to the front. In my car, for my driving, the rear already seems weak so going to a larger rear bore seemed like a bad idea. Before I went to a two master cylinder solution I thought I would try to save my original MC.
The bores cleaned up nicely with a master cylinder hone. Many are available, do a search. A stock rebuild kit is available from RD.
I purchased a BMW W0133-1954617 dual remote MC reservoir.
Fabricate a brass place with a soldered in hose bib to cover the large / front hole. Tap the MC and use clearance holes in the brass plate so in can be installed from above. Use the new o-ring / gasket (from the rebuild kit) as the seal between the brass and the master cylinder. This is essentially the same system that is used with the original plastic tank.
The front hole can be tapped with a 3/16” pipe tap. I had to shorten the length of my pipe tap (grind off a little of the end of the tap) so I could cut a wider thread at the top to seal with the brass fitting I used. Pipe specs are somewhat loose so you may or may not need to do this with the brass fitting that you use. I used Teflon pipe tape to lubricate the joint. Do not use too much to prevent contamination of the brake fluid. Both these connections are low pressure and easy to make without leaks.
The remote reservoir can be mounted next to the cabin fan.
