This is the result;
http://www.gadgetmax.co.uk/dragon/joystick/P1080068.JPG
I took out this little chap;
http://www.gadgetmax.co.uk/dragon/joystick/P1080063.JPG
And replaced him with this bigger chap;
http://www.gadgetmax.co.uk/dragon/joystick/P1080064.JPG
Which I bought from ebay;
https://www.ebay.co.uk/itm/255760843061
Service Arcade button Push Button 15mm Service White Red Black Blue Green
I checked the dimensions carefully before buying and it fit's perfectly after drilling the hole out larger with a stepped drill.
I hope the photos show up, if not then use the links.