Just Sharing This Brake Master Cylinder Trick

I have been looking for an original master cylinder for a 1970 Dart Manual Disc Brake system.
I want to keep the original cast iron MC for the original look and still have to decide on the piston diameter. I have read from others that 15/16 is a good choice?

During my research I read product descriptions for aluminum MCs being used because of rust issues? Is this the main issue?

If this is an issue for those using cast iron MCs:

1. Years ago I ran into problems with DOT 3 fluid getting on the car and ruining my engine compartment and fender paint.
2. I used Dot 5 to solve this.
3. Since Dot 5 doesn't harm paint I have hand painted with a small brush Rustoleum brown primer inside the MC reservoirs carefully not to get it in the small return ports for the piston. The DOT 5 will not harm the Rustoleum primer and it is excellent rust protection for the inside MC reservoir.

It has worked great for my two boat trailers that sit outside, three restoration cars that have sat for over 30 years with never a problem. It takes patience and it is best to apply the primer when the cylinder is brand new but you can easily degrease the inside wiping it with some lacquer thinner.

Have at it or not - JUST SHARING