Not able to extend the Help menu - eclipse

Question

I want to add from an eclipse plugin a Request Support button to the Help menu.
I tried first from a *.e4xmi file and now I tried from the plugin.xml but still can't make a button to appear under the Help menu.
I got the menu URI with the help of Eclipse Spy Plug-in.
The content of plugin.xml:
<extension
point="org.eclipse.ui.menus">
<menuContribution
allPopups="false" (tried with true and same result)
locationURI="menu:help?after=about">
<menu
commandId="com.plugin.RequestSupport"
id="requestSupport"
label="Request Support">
</menu>
</menuContribution>
</extension>
<extension
point="org.eclipse.ui.commands">
<command
defaultHandler="com.plugin.handlers.RequestSupportHandler"
description="Opens up default e-mail client with preset basic informations"
id="com.plugin.RequestSupport"
name="Request Support">
</command>
</extension>
What am I missing?
SOLUTION from greg's answer:
<extension
point="org.eclipse.ui.menus">
<menuContribution
allPopups="false" (tried with true and same result)
locationURI="menu:help?after=about">
<menu
commandId="com.plugin.RequestSupport"
id="requestSupport"
label="Request Support">
</menu>
<command
commandId="com.plugin.RequestSupport"
id="requestSupport"
label="Request Support"
style="push">
</command>
</menuContribution>
</extension>

Answer 1

This is what 'Check for Updates' uses:
<extension
point="org.eclipse.ui.menus">
<menuContribution
locationURI="menu:help?after=additions">
<command
commandId="org.eclipse.equinox.p2.ui.sdk.update"
mnemonic="%Update.command.mnemonic"
id="org.eclipse.equinox.p2.ui.sdk.update"
icon="icons/obj/iu_update_obj.png">
</command>
Which is adding after the 'additions' location.
The code which creates the help menu defines a lot of locations:
private MenuManager createHelpMenu() {
MenuManager menu = new MenuManager(IDEWorkbenchMessages.Workbench_help, IWorkbenchActionConstants.M_HELP);
addSeparatorOrGroupMarker(menu, "group.intro"); //$NON-NLS-1$
// See if a welcome or intro page is specified
if (introAction != null) {
menu.add(introAction);
} else if (quickStartAction != null) {
menu.add(quickStartAction);
}
menu.add(new GroupMarker("group.intro.ext")); //$NON-NLS-1$
addSeparatorOrGroupMarker(menu, "group.main"); //$NON-NLS-1$
menu.add(helpContentsAction);
menu.add(helpSearchAction);
menu.add(dynamicHelpAction);
addSeparatorOrGroupMarker(menu, "group.assist"); //$NON-NLS-1$
// See if a tips and tricks page is specified
if (tipsAndTricksAction != null) {
menu.add(tipsAndTricksAction);
}
// HELP_START should really be the first item, but it was after
// quickStartAction and tipsAndTricksAction in 2.1.
menu.add(new GroupMarker(IWorkbenchActionConstants.HELP_START));
menu.add(new GroupMarker("group.main.ext")); //$NON-NLS-1$
addSeparatorOrGroupMarker(menu, "group.tutorials"); //$NON-NLS-1$
addSeparatorOrGroupMarker(menu, "group.tools"); //$NON-NLS-1$
addSeparatorOrGroupMarker(menu, "group.updates"); //$NON-NLS-1$
menu.add(new GroupMarker(IWorkbenchActionConstants.HELP_END));
addSeparatorOrGroupMarker(menu, IWorkbenchActionConstants.MB_ADDITIONS);
// about should always be at the bottom
menu.add(new Separator("group.about")); //$NON-NLS-1$
ActionContributionItem aboutItem = new ActionContributionItem(aboutAction);
aboutItem.setVisible(!Util.isMac());
menu.add(aboutItem);
menu.add(new GroupMarker("group.about.ext")); //$NON-NLS-1$
return menu;
}
(from org.eclipse.ui.internal.ide.WorkbenchActionBuilder)
All the addSeparatorOrGroupMarker, new Separator and new GroupMaker calls define ids to can add after.