Vibration caused by worn shock absorber?

[TNW]

I've got a Gen 1 997 C4s which had an unfortunate night-time interface with a lump of timber that had dropped off a lorry and was left across the slip road to a motorway. There was no visible damage, but following this the car developed a vibration at about 100 Kph, give or take 10 kph either way, much like when a wheel is out of balance.

The diagnosis from the garage (a very well trusted Porsche specialist here (there's no point going to the local OPC) was that one front wheel needed to be straightened and the other replaced as it was out of shape in two directions. This has been done and the car is now pretty much back to as it should be, but there is still a slight vibration/wobble through the steering at around 90 - 100 Kph.

They are now telling me that they feel the remaining vibration could be cured with two new dampers. I've got no reason not to trust them from past experience, but this does seem a bit odd to me. I'm no mechanical expert, but I struggle to see why a damper would have this effect at a specific speed and not get worse the faster the car travels. Any views if this diagnosis seems like a bit of a guess or ideas of what else should be checked first?

Thanks

Edited by TNW on Friday 3rd April 18:55

[Trev450]

My first step would be to have to wheels re-balanced, then if the issues persists, maybe take it somewhere for a second opinion.