+1 - unless it is bought from someone whom you believe to be telling the truth when they say it has recently been serviced (ie a vintage dealer that offers a 1 year guarantee)I believe that the only dumb question is the unasked one. You instincts are correct it will need a service and for the reasons you stated.
The problem is you can not always believe the seller. If they are selling on price they are not paying to have it serviced. And I have had seemingly reputable jewelers claim they can clean watches with out disassembly. So what a service even is can be questioned.Thanks guys. I will be sure to ask if they had it serviced. If they haven't, I'll probably pass on it.