A fresh spill in Wisconsin could spell more troubles for the Canadian company that imports more crude into America every day than Saudi Arabia or Mexico -- including heavy fuel from Alberta's politically volatile oil sands. The Friday leak of 50,000 gallons of light crude from a Wisconsin pipeline run by the U.S. subsidiary of Enbridge Inc. came on the heels of a National Transportation Safety Board report that blasted the company's handling of a 2010 spill in Michigan that ranks as the most expensive U.S. onshore oil disaster. Environmental groups fighting Enbridge's proposed reversal of a pipeline that they say could run heavy oil sands crude to East Coast ports promptly pounced on the new spill.