I just went through the Domestic - International routine in BOM. The whole process is very unpleasant.
Arrived with 9W and had to search for the door in the corner of the room where the luggage is collected. In my opinion it is not clearly marked. But at least there are a lot of signs that tell travelers with international connections not to leave the building.
Once I found the door in the corner all the luggage had to be x-rayed again and my information was entered in some kind of log-book by hand. That slowed down the transfer quite a bit. Luckily there were only a handful of passengers!
The free bus drives inside the secure area of the airport. There is a guard inside the bus besides the driver. It takes a little while for the ride, maybe 10 minutes.
Once I arrived at the international airport we were asked for tips when collecting our luggage from the bus's trunk. Other "guides" with official looking ID's around their neck were forcing their help on me. My connecting flight was with BA which departs from "D". My "guide" was semi helpful in directing me, so I gave him a little tip.
Since my flight did not leave for another 6 hours I was refused entry into the terminal building. There is an air conditioned waiting room at the very end of the airport (just past the BA entrance) where I was able to wait comfortably until I was allowed into the terminal. It cost R70 to get into the waiting room. There is a fast food stand and a bunch of seats in the room.
4 hours before my flight departed I was allowed into the terminal, checked in and waited some more in the BA lounge.