Heat oil and butter in large pan and saute onions for 5 minutes. Add diced carrots and wine and cook on low for 20 minutes.
Drain clams, reserving juice. Set aside.
Add potatoes, reserved clam juice, 1 cup bottled clam juice and enough water, if needed, to barely cover potatoes. Stir in bay leaf, thyme, salt, pepper and Old Bay seasoning. Bring to a simmer and cook, covered, until potatoes are almost done, 10-15 minutes.
Heat half and half in seperate pot until steamy, but not boiling.
Add fish to soup pot along with clams, shrimp and crab. Stir in hot cream and cook on low heat, uncovered, until fish is just cooked through and seafood is heated. DO LET BOIL!!!
Ladle into serving bowls and sprinkle with parsely.