1) In a deep-fryer or Dutch oven, add oil to fill 2/3 of the way and preheat to 190C.
2) In a saute pan, add 2 tbsp oil. Add onion and garlic, and cook for 2 mins over medium-high heat. Add cabbages, spring onion, carrot, oyster sauce and salt and pepper, to taste. Cook over high heat for about 2 to 3 mins. Remove from the heat, drain excess liquid, and cool. Fold in crabmeat and mix to combine. Separate the sheets of spring roll wrappers, and keep under a slightly damp towel. Place 2 tbsp of crabmeat filling on the wrapper. Fold nearest edge of wrapper over filling; fold left and right corners toward the centre. Roll tightly and seal with the egg wash. Place the spring rolls into the preheated oil and fry until golden brown. Place on paper towels to drain. Serve with pickled ginger vinaigrette.
3) For the pickled ginger vinaigrette: In a mixing bowl, combine dashi, sugar and rice wine vinegar. Transfer mixture to a blender and add fresh ginger, pickled ginger and salt. Slowly add salad oil to the blender. Serve chilled.