Did you get a schematic with it? You are going to want one of those. There are a bunch of things that run the score motor and one of them is staying closed.

If you set all the score reels to 1 do they reset to 0? If not fix those first. Is there a bonus unit and is it resetting? Check that too. Only when we can see the part of the schematic with the motor on it will be know all the things it could be.

It would be nice to post a quick video of it doing this (include the playfield and the backglass) so we can see if anything sticks out.

You can buy schematics here: www.pbresource.com/mansch.html

this will be helpful too http://www.pinwiki.com/wiki/index.php?title=EM_Repair

you haven't mentioned if you have a schematic. It is remotely possible for you to fix this without one but if it's not something obvious you are going to want it to help you track down why certain things are happening.