Not sure difflock is always going to get you out of trouble?
Lane from Stokenchurch to Crowell (ok - so it had a road closed sign....) was polished to a glass finish under a powdering of snow. Headed down, I had escape route planned into the verge, and used it. Back end just swung round and downhill on its own. Headed back up 2 low diff locked on tickover, but eventually just slid back. Couple of pirouettes later lined it up on verge and crawled down to find a sandwich of Dsco with trailer, transit, with the filling a Police 4x4!!
Inched past without sliding into them - got down in one piece, but no difflock rescue uphill there. Fun though! A
[but of course once you are sliding then engage the gear appropriate to the direction of travel (!) and get the wheels up to speed to stand any chance of grip - locked on the brakes or going the other way they'll slide all the better I'm sure!]