my old 1981 240 had a m46 gearbox and 1 hour into a 4 hour drive the speedo & OD stopped working (cable speedo) i stopped at a highway rest stop and tried looking at the speedo cable connection but couldnt see anything wrong...i continued the 3 hour drive and had it checked the next day ....it turned out the cable had unscewed itself and unloaded all od and box fluid....when i got home i used the hole in the cable/nut to lockwire it to the box..i cant believe a mechanic would simply screw it back on again, it was obvious it needed to be locked...daryl from aussieland.....the box worked fine for a long time after that