Just had a good look at the ehu. I lubricated the plug with some silicon grease, it didn't make much difference.
If you haven't actually looked at the plug engagement mechanism, it's worth a look. You can get a good view with a tourch. My problem is it seems to be stuck in. It latches in when thr plastic peg on the flip up cover drops over an edge (or maybe a hole) in the connector. The blue push down lever, lifts the flap so you can pull it out. Mine doesn't seem to lift it that well, all the plastic just flexes and doesn't lift the flap. If you push in and move it a bit it disengages and it comes out. It feels like the blue lever could break.
More tinkering required, I'll try the 90º plug as well.