Had an email from smiths today. They said send the gauge in and they will mod the software on it to add dampening. The fuel gauge should be dampened but apparently sometimes they assign none dampened software to them. It could be £25 but if it turns out it has the none dampened software (it does) it will be a free alteration.
Either way they can sort it with no need to add extra parts or alter a thing. Peter the software engineer was very helpful tbf.