Have worked 36 years for same company. 18 years have been on salary for 40 hrs. per week. 3 years ago hrs. were cut to 35 but still paid for 40

Probably not.  If you are paid a "salary," that pay compensates you for the number of hours worked in a workweek.  It could be 40, or 50 or 35, but the salary covers all hours worked.  The real issue here may be "was the employer permitted to pay you a salary?"  Salaried employees are usually those who are "exempt" from the payment of overtime under federal and state wage and hour laws.  If your job duties would not have qualified you as an "exempt" employee, your employer should have paid you on an hourly basis, not salaried.  Either way, if you have been paid a salary it is not likely you would have been "overpaid" and owe the money back.