Seamaster 321 - gaining 5-10mins per day

Hello Omega fans!

I'm looking at buying my first vintage Omega (cal.321) and I'm hoping you can provide advice....

The watch I've found listed is gaining approx 5-10mins per day. Should this watch be avoided?

I've factored into the purchase price the cost of getting it serviced, but is it likely that there will be higher costs to repair?

I appreciate this is an impossible question, but looking for guidance on whether anyone else would buy a 321 with this issue.

I'm not sure if this can affect the 321 in the same way, but in my experience with a Zenith 28,800, demagnetizing it helped things dramatically

Would not stop me. Just adjust the price...

Old watchmakers easily fix bumped balance springs ($10 here), if you have a movement photo of the balance, it'll also help you in finding a better estimate - just moving a rod a little bit to one direction could also get it within ~20 seconds a day too