Hi, Antony,
On the stylesheet, c5ddropdownmenu.css, there are a couple of items that could be cleaned up a bit.
1) The property, #nav li {height:90px}, is unnecessary and should be deleted. It is causing the clickable area for the horizontal menubar items to extend about 50px below the menubar. (You can tell by the pointy finger cursor.)
2) #nav li:last-child only needs to contain those items that are different from the ones already listed in #nav li. In this case, the only one that is different is {background:none}. The other properties can be deleted from this selector.
Code:
#nav li {
/*great place to use a background image as a divider*/
cursor: pointer;
float: left;
margin: 0 ;
padding: 1px;
height: 90px; /* DELETE. Unnecessary. */
display: inline;
background: url(../images/nav-separator.png) right center no-repeat;
}
#nav li:last-child {
/*remove divider from last menu item*/
cursor: pointer; /* DELETE. Unnecessary duplication. */
float: left; /* DELETE. Unnecessary duplication. */
margin: 0 ; /* DELETE. Unnecessary duplication. */
padding: 1px; /* DELETE. Unnecessary duplication. */
height: 90px; /* DELETE. Unnecessary. */
display: inline; /* DELETE. Unnecessary duplication. */
background: none;
}
3) The sixth list item, "P R Es", has a left-over id of "dummy7". You can safely delete that id. 
4) Finally, the list item, "NZ" > "Order Form", contains what I presume is a test id="radius". Don't forget to delete it, too.
Noteworthy... you have done a smashingly nice job of cleaning out the unnecessary classes and ids from the c5dmenu.php menu file. It's actually easy to read, now!
Cheers
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