Plugs take some getting at, a lucky few with small hands (!) manage without front mudguard removal, the rad is hinged and swings out of the way just.

Given awkwardness of access I suggest you fit (and forget) Iridium plugs like many other owners, also be very sure you've fully seated the plug sockets.

If you get stuck on any servings Le dude on you tube he is mint and there are lots of vids to look at. Welcome to forum.