Shimano roller brakes: differences between each model and interchangeability
For all I know the roller brake mounting mechanism is the same for all the Shimano roller brake models and all use the same cable pull ratio. 

Different (ly priced) models have different stopping power adn cooling (although none are recommended for long braking on descends etc).

Cleaning and regreasing them usually helps. Shimano roller brake grease works fine in my experience, although I suppose (haven't tested) that molybdenum disulfide grease from a store should work fine (NLGI 1 hardness seems apropriate).

Made a video showing how to dissassemble, clean and reassemble a roller brake (lubing is not shown). 

There's also a long and detailed explanation of the Shimano roller brakes on Sheldon Brown website.