Bob Wight wrote:

I can’t tell for sure what’s happening in your picture but there is a retaining screw in the middle of the reed plate that needs to be removed.   I can’t tell if you removed that screw or not because it’s covered up with some kind of gunk.  If not already removed, that screw needs to come out to get the reed plate off.   See attached markup of your picture.

This was it!
Thanks gents.

It appeared to be a bug rust blob – but it was a slotted screw.