To get hold of 3 ended grounding strap that VW used - go to some place that sells industrial use wires, They have it in flat and round versions - its pricey though, most probably you would need to take a sample. In Karachi there is a market on Frere Road near Burns Road - I bought a few feet from there and made some nice looking pieces. buy a copper pipe and have a blacksmith braze the wire onto it - twist around a pipe of similar size of the terminal to make it fit the battery and drill through to accept a bolt and nut.
To clean out the rear - nmshaikhs scissors method is best - clean it out with detergent (AJAX and not Bonus Powder) - clean the battery cradle with baking soda to neutralize any acid, dry and spray some paint to seal the area. BTW get hold of a DIN style battery with a vent pipe on the side - you can attach a rubber pipe and exit it somewhere outside the car.