Just a quick one for anyone planning to do it from the South (Loch Voil end) but doesn't know - there is currently a diversion at the start of Beinn Tulaichean from just after the farm as there are construction works going on at the river (which you would normally follow in) .
Instead of turning North just after the bridge and following the route on the WH route you continue SW for about 500m through the next farm then you see a diversion sign pointing North
Basically this takes you across bogs, bogs and more bogs on the other side of the high fence. You can head North and met the path further up but be prepared for some wet ground