I've looked all over, and I just can't find a clear answer on the Eclipse pages on upgrading milestones (or really upgrading general) What is the correct way to upgrade an Eclipse 4.3 milestone to the next milestone, for example 4.3 M5 to 4.3 M6.
Even after adding http://download.eclipse.org/eclipse/updates/4.3milestones, the core Eclipse components do not show up when checking for updates.
Do I need to explicitly install the new milestone and then copy over the packages even for milestones (as described in https://stackoverflow.com/a/11264210/255961)?
There is a related question at Upgrading Eclipse IDE for Java EE Developers, but its focused on 4.2 and complicated with the general question of fixing the Juno slowness rather than how to upgrade.
You are doing it right. I've just verified upgrading a M3 SDK, which worked fine without adding any new update sites to the 3 pre-configured ones.
You may have installed additional third-party plugins, which themselfes have dependencies specified with version ranges. Such plugins would prohibit an upgrade, as P2 will not install upgrades that break currently working dependencies.