why are automatics so messy

The actual reason given by Chrysler, is because when they bought the the Torque Flite transmission design and comissioned the automatic transmisson to be made, they were convinced that it would not need to be maintained during the lifespan of the car. Remember, the oils used were not multi-grade, gasoline and the cars would not push nearly as many miles on the same drivetrain, as we see now.

I put a drain plug in the 904 pan on the Scamp, even though it's coming out for an 833 soon.

The best way that I've discovered to drain a trans pan is to pull all of the bolts from it, except for two at the ends of one side that you leave tight, pry on one corner and let it drain from that corner. If you loosen the two bolts up a bit, it will allow more flow. Sometimes I leave something, like a flat blade screwdriver wedged in it and the fluid will follow one corner.