people didn't find the "download diff" link

Did they (a) see the diff displayed on the page, but not see the "Download diff" link in its header, or (b) not see the diff at all?

If (a), maybe move the "Download diff" link from the left of the diff block to the right, and/or remove the grey background from the header.

If (b), it's probably because of the link styling. Links are most obvious if they are consistently blue and underlined. Many sites get away with styling some links differently from others, many sites get away with using a color other than blue, and many sites get away with removing the underlining, but doing all three at once may be going too far.

I wonder if an icon to go with the diff against link in the heading info would help. Most everything else that's a link has one. I wonder if the lack of a diff icon causes it to just not "line up" visually with the links above it.

I do think that floating the download link to the right looks much better and clearer as well.

I think putting an icon against every link is an antipattern, and the
new draft style seems to go away from that in general, so we shouldn't
rely on that. But I suppose a specific 'download' icon could be
generally worthwhile and might help here. (It won't be so common as
to be meaningless, like the pencil is, and it will usefully warn the
user something different is going to happen - a download rather than a
web page.)

This is a fairly important link and there is only one per mp page, so
perhaps it belongs in the 'major links' region of the top right
portlets?