Live in a house with a shared driveway with neighbour. Both houses have a garden wall running along the bottom of driveway. Our neighbours house is a rental property and the landlord knocked the door recently wanting to rebuild the wall as it is unstable. I had not noticed this, but when we investigated we discovered that the wall has split along the first line of bricks beginning at the side by their gate to about a foot along our side. It very much looks as if it has been hit by a vehicle or something like, but this isn't obvious enough to say for certain. We replaced our gate a couple of years ago and the problem certainly wasn't there then. We think it probably happened when the neighbours house was being renovated and had a lot of big vans parking on the drive.
I think they want us to share the cost equally but the timing is rubbish for us - we have other priorities at the moment. However, the wall is a little unstable and so will need rebuilding. Next doors landlord is in a rush to do it. AIBU if I only offer to pay something towards the cost but not half as in our opinion they may have caused the damage?