If you are getting a clunk when going from reverse to drive or drive to reverse it can be an indication of worn driveshaft splines.
When I replaced the driveshafts in my 2001 2.4 V70 (220Kmiles) a few months ago the clunk disappeared. It seemed more time efficient and a lot less messy to change the both shafts rather than just replace the CV joints on both sides as given the mileage I thought there might be some play in the splines. The replacement driveshafts from J&R (
https://www.jandrcvjoints.co.uk/cata...ive-shafts-509) came supplied with new bolts.
Re the bolt head size, my T5 has 13mm N/S and 14mm O/S - I'm told the bolt head size spec was changed some years ago so maybe someone has replaced one of the bolts when a CV joint was changed.
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V70 SE 2004 2.3L T5 Geartronic, C70 2005 2.0T Automatic, Sold 2.4l 20 Valve Automatic Torslander Sold 854 GLT 20v Auto