close coupled cistern leak?

i have just had a close coupled toilet fitted, at first there was a small leak out of the front of the cistern which ran down the wing screws that hold the cistern on, i replace the doughnut and this stopped, but now it is leaking into the pan, it is not going down the overflow pipe, im pretty sure its not leaking through the new doughnut, i've took the cistern off a few times and checked everything and now im at a lose end. thanx.