I have seen these components on other Gallagher fencers and have not been able to determine what they are. I bought a packet of what I thought were ceramic capacitors at a radio rally, they measured about 5pF so I do not know what they are.
There used to be a website put on by a UK government organisation showing how to erect a fence with an inductance. I have not seen it lately.
My brother used to have fencers damaged by lightning and I made an inductance, six turns of fence wire about 300mm diameter, spaced about 25mm mounted on a wooden cross. There were no more damaged fencers. Whether this was just coincidence I know not, but worth a try.
One Gallagher fencer had a PCB plugged in at right angles to another board. The current objected to going the long way round and sparked across the corner, producing ozone and rotting the plastic holding the transformer together. I soldered gently curved links across the contacts and used a twig to hold the transformer together. This seemed to work but the fencer made a very loud click. A better bodge would doubtless quieten it.
I could not find details of the M8000.