Mines was pretty dirty and may have had a blocked breather so ah decided to clean it.
Here's how ah did it....

The fuel cap...



flipped it over to find two screws...



undid these and took the plate off to reveal this...



then ah took off the locking arm notin' which way it came off...



and removed the big seal...



and the big wavy washer...



last thing ah did was removed the small ring that sits under the lockin' arm (could've done this at the start!!) then undid the two screws and removed the part with the lock and breather...



Gave everything a good clean and made sure the ball bearing wasn't stuck and moved freely on the spring...



Then it was just a case of stickin' it back together in the reverse order...









That's it, job done