Many chaps from marlinowners have had this issue [front sight off centre right or left ]I personally did not have these issues ,mine were receiver alignment issues on 91 serial numbered guns .I would send it too Gravel ,you will have to pay postage ,but Gunsmiths are also expensive .It is your call ,please dont listen about those Marlin guns not shooting accurately .They will follow most bolt guns with ease I have 3 in 308mx and 338 mx that will rival any bolt gun in 308 and 338 class period ,,,,[.75 @100yards] ,when not being hammered with sks brass or left alone with no noise around me
She also re-imbursed my postal fees ,so ask her to help you out