4000 running fast by 30 mins a day

My treasured mid size 4000 (non automatic) WF1212-KO jumped 20 minutes sometime during the day and has since consistently gained 30 or more minutes a day.
The only thing I can think off that may have caused it is by using a hand held spot welder for a day that runs at around 6000 A at about 1.5 Volts.
Have my learned readers any advice (other than not buy a rusty TR6!).
TIA
Bill

Can try getting it demagnetized, but it's entirely possible some of the gears have been damaged. Easy enough to do a movement swap with a compatible, less easy to get an exact replacement movement however.

I don't think it's wise to demagnetize a quartz watch.

Pics of the TR! Wife’s first driving lesson was in a Stag.