Welcome to the forum Baz.
Magnetization is one of many causes of fast running. Wrong or short hairspring fitted on, is another possibility. We just can,t be sure.
Disclose the caliber, post pix of the movement helps those who may, like me, be unfamiliar with the piece.
I can not see it being that old. Pendulum does not look that old along with other parts. Certainly been restored. Not sure how the note came with it? Maybe look for those names is it possible it is not a date?.
Sometimes this is the "reward" for cleaning well.
If you do not want to change to a thinner mainspring (the usual remedy), you can open the banking pins a bit. This will take more energy from the escapement during unlock.
I'm new to this group but have been watching with interest Marks videos for some time.I'm 65 and am a bit of a watch fan, in a modest way.
I bought a Tag Heuer Aquagraph from e-bay and it is running extremely fast, and when I say extremely 5mins an hour! The piggy back chrono is running similarly fast too.
Any advise would be helpful, was wondering if it may have been magnetised even or do you guys think it just needs a full service.
Any help greatly appreciated.