Combine Is Large Saucepan, Vinegar, Water, Onion, Celery, Carrot, Peppercorns, Cloves And Mustard Seed. Bring To Boil. Allow To Cool To Room Temperature. Pour Marinade Over Roast And Allow Roast To Marinate For 2-3 Days, Turning Occasionally. Remove From Marinade And Dry Well. Sprinkle Meat With Salt And Pepper And Saute In Olive Oil Until Browned On All Sides. Add 2 Cups Of Marinade, Cover Simmer For 2 Hours. Remove Meat And Keep Warm. Add Water Until You Have About Two Cups Of Liquid In Pan And Stir In Flour And Sour Cream, Cook Until Liquid Is Thickened. Serve Over Meat.