I just bought my 1987 740 turbo wagon, the only thing that needs attention is the overdrive on the automatic transmission. The red arrow light is on in the dash and the car will not go into overdrive, it's as if it is locked out. The button on the shifter has no effect on the red arrow light. Gears 1,2,3 shift ok, slightly rough but it will not go into o/d. The friend that I bought the car from said it is one of 3 things, switch, relay or actuator, he also suggested I replace ALL underhood vacuum lines. Any suggestions? Thanks, Tom.