The 4th gear switch that is supposed to 'lock out' O.D. in first through third gears is malfunctioning such that O.D. can now be engaged in any forward gear and, I suspect, reverse. So long as I don't inadvertently push the button when the tranny (M46) is in reverse, is there any harm in this? 3rd + O.D. produces an interesting ratio that is sort of a compromise between the range of 4th gear and the torque that is available in 3rd gear. In traffic, this does away with the annoying gear change (3rd to 4th and vice versa) that is usually required between 35-40mph, while retaining the responsiveness of 3rd gear. But I don't want to damage the tranny or O.D.