Here you see the smaller palm size grease gun commonly known as the "pom-pom" gun. The one pictured here is the currently available plastic aftermarket unit, but should work just as well as the original brass units.

This is a nifty tool that is perfect for installing gear oil in the MGA steering rack. It holds just the right amount of oil for the original fill, and is very easy to use. For initial assembly and first fill of the rack, you can fill the palm gun once, pump it all into the rack, and toss the empty gun into a drawer. For future use, if you only want to add a little oil to the rack, you can put a couple ounces of oil in the palm gun, pump it into the rack, and toss the empty gun into a drawer. I wouldn't recommend trying to store the gun with any oil in it, as it seems to leak a little in storage, no matter what the orientation.

If you want to take a grease gun with you on a long road trip, this one will dispense grease just as well as oil, and makes a smaller bulge in your traveling tool kit. With a little luck it might actually contain the grease in storage without dribbling, but I wouldn't count on it, especially if it gets hot in the sun (or in the boot of your car sitting in the sun).

This tool is available from most British car parts suppliers. The original brass bodied version may show up on eBay occasionally. I have no personal experience with the original ones. If someone does have one, I would appreciate a user report.

Addendum, January 2013:
Since someone asked, it is not supposed to snap onto the Zerk fitting like a standard grease gun. The interface fitting has a funnel shape end. You press it up against the Zerk fitting and push/pump with the palm of your hand, which is why it is often called a Palm Gun. It works well for putting oil in the steering rack, which is all I ever use it for.