In a deep bowl or crock combine the soy sauce, cooking oil, molasses, ground ginger, dry mustard, and minced garlic.
Add meat to marinade mixture, turning to coat.
Cover and refrigerate overnight, spooning the marinade over meat occasionally.
Remove roast from bowl, reserving marinade.
Place roast, fat side up, on rack in shallow roasting pan.
Insert meat thermometer.
Roast at 325° till meat thermometer registers 140° for rare (about 3 hours); 160° for medium (about 4 hours); or 170° for well done
While the meat is roasting, baste several times with the reserved marinade.
Remove roast from oven; cover with foil.
Let stand about 15 minutes; remove strings and carve thinly across the grain.