The trick to Golden Bra is to save right before you enter a cave, the first random map to get to the cave doesn't matter. They are randomized, but they randomize again when you enter the cave.
When you enter the cave, hit the menu button, if it says Random Cave #4, then you are good. If it says anything else, hit F5 and reload. Rinse and repeat until you get to random cave #4.
Anything else is a complete waste of time. Cave #5 is identical to 4, but it's the rigged chest. I got it 5 freaking times, and never 4. The need to hit F5 so often in this game is it's biggest flaw in my opinion. Grinding isn't as bad if you are at least gaining something, but here random drops or random caves are way to rare in relationship to wasting a few hours with gaining no items or experience. Don't want to be harsh, but this really is a giant flaw in the game design.