A mechanical 'breaking noise' doesn't sound good. It's hard to diagnose a problem online without being there to see/hear the vehicle. But .. it may be that your clutch pressure plate has broken/ release/throwout bearing has broken?
It's difficult to see why the master cylinder should leak - unless it was incorrectly fitted in the first place?
Just to check ... The master cylinder is in the engine bay/compartment and is where you top up with clutch fluid. When a master cylinder fails it usually results in no pressure at the clutch pedal, not a leak.
The clutch slave
cylinder is the one that does all the work. When you press the pedal hydraulic pressure is sent from the master cylinder to the slave cylinder - which then pushes the release/throwout bearing against the clutch pressure plate and 'disconnects' the driven plate .. allowing you to change gear.
The slave cylinder is the one that does all the hard work - it is located somewhere where engine and gearbox mate together, usually at the bottom right/left. It's usually the one that fails/leaks. It's quite easy to replace..
I don't think it is anything to do with reverse gear. It's more to do with the clutch pedal being depressed - and, I would suspect - something has failed.
The link below is generic images of a clutch:
clutch diagram Google Search
Basically, a clutch is 3 parts. There's the 'pressure plate' which bolts onto your flywheel. The pressure plate is a 'spring'. You depress the clutch pedal and the release/throwout bearing presses onto the centre of the pressure plate causing the 'fingers' - the springs - to bend back and take pressure off the driven plate - which is the link - the drive - between engine and gearbox.
If you have a leak your clutch will not work. This causes a 'grinding/crashing' noise when you try to change gear. The first thing you should do is check where the leak is coming from and do something about it.
The 'noise' that you mention may be due to the fact that the gears are 'grinding' as they try to mesh together without the use of the clutch.
The first thing you should do is check why there's a leak. It's difficult to see why a new master cylinder is leaking unless it was incorrectly fitted and damaged (pipes incorrectly connected..).
If it's the slave
cylinder that is leaking - replace it. Easy job.
If Master cylinder and slave cylinder are ok - you have to look at your clutch unit. A clutch is always replaced with 3 parts ... throwout bearing/pressure plate and driven disk.