we have just moved house and noticed a small leak from the rubber gromit at the top back of the toilet where a plastic pipe comes out and goes to the bottom of the cistern,has this gromit have to have some type of mastic or sealer to stop it leaking
Flushpipe connector Mr Fishing.
No, it's just a push fit. With the separate cistern and pan, the flushpipe is often not cut to the right length. It should come out of the cistern and enter the pan in a right-angle.
I would unscrew it from the cistern, pull it out of the pan, and check the angle with the pipe loose (no connector) to make sure it's not being strained at the wrong angle.