Any one no of it is hard and if you need any special tool to change it?
It's the cap on the head

 

sounds like a core plug (without me goin in the garage to look at mine)

you can knock them out with a hammer and punch, just hit 1 area so it spins and then You can prise it out

You can then carefully knock a new 1 in using a socket or similar tool

 

Yeah it's a core plug for expansion. Should tap out and fit a new one.

 

Ok lads cheers