Without wishing to hi-jack your thread, I have just rectified a long, ongoing issue with my D-type OD. It turns out that there was so much wear on the levers that operate the OD isolator switch and the reverse light switch that there were grooves in them,(the levers). It didn't make any difference to the operation of the reverse light but the OD would periodically keep jumping in and out especially under load or at speed. I had tried everything to stop this happening and as a last resort I changed the top cover. The one I had been using was off a spare gear box I had when I first obtained the OD, which was off a Sceptre so I obviously had to put a Commer top cover on in place of the remote.
The top cover I now have on the gearbox is off the original gearbox which was on the van initially and had only covered 44k and didn't have any switch wear. I can't believe the difference it has made, it almost feels like a new gearbox as you go through the gears and no more jumping in and out of OD which is shear luxury and piece of mind when on a motorway or trunk road. It's only taken me 3years of faffing around to eventually sort out.