What make of calliper is on your Roadster? If one side is rusting up this indicates that the piston(s) on that side are sticking. You can usually detect this is happening as when braking lightly you will feel a slight judder from the front and then when you brake harder it will go as you overcome the sticking. If this is the problem then the least you would need to do is strip the callipers and replace the seals. However some makes of calliper can suffer with time from casing distortion which the causes the pistons to snag, you cannot do anything about this, apart from get new callipers.
My advice would be to carefully inspect them, and have a chat with Peter at Mulfab, he will be able advise and help whatever the end solution is.
