Valvoline (NYSE:VVV - Get Free Report) announced that its board has approved a share buyback plan on Tuesday, September 29th, RTT News reports. The company plans to repurchase $175.00 million in shares. This repurchase authorization allows the basic materials company to repurchase up to 4.8% of its stock through open market purchases. Stock repurchase plans are typically a sign that the company's board of directors believes its shares are underv…