When I changed my axle to a LSD I didn't change the master cylinder from the old drum brake unit. I have very good brakes so I'm going to say that it's probably not needed.
The rear axle vent sure had a lot of discussion but I think it's fairly simple. Some axles are in better condition than others and this may cause them to produce more heat. Don't panic if your is one of the ones that leaked - it may not mean there's any problem with your axle at all.
6.3's have the vent on the right tube and most everything else had it on the side of the diff housing - the 4.5 seems to be alone on this configuration but then it has a cooling tube. The tube is the key here as the moving crown gear throws all of that hot oil right at the upper tube opening. Without this tube in place the oil can splash back against the vent tube opening. Moving the vent to a location far enough away from splashing oil will mitigate those problems.
