[A Cobra guy]

I built my EM about 12 years ago so it is likely similar to what you have MJ. It came with the dual master cylinder setup so the brakes are manual. After a good deal of tinkering I now have brakes I am happy with. To address your issue the plastic resivoirs have never been an issue. the dual MC's allow the brakes to be balanced nicely.
What I did notice was the pedal always felt spongey. I finaly figured out the entire front of the foot box was flexing. The entire pedal assembly is bolted to the fiberglass. I reenforced the front of the footbox with some steel. the f-box no longer flexes and the pedal feels much better.

On a seperate brake issue I ordered my frame with the 11" granada rotors and the single piston calipers on the front. They were terrible! I found a brake kit with aluminum hubs, 11.5" rotors and 4 piston wilwood calipers. This new setup is great.