Buyers hope to restore reputations of once promising, now struggling Sonoma wineries.Two of Sonoma County’s best-known producers—Buena Vista and Gary Farrell Winery—have new owners, thanks to the financially troubled Ascentia Wine Estates’ efforts to thin out its portfolio of wineries. Buena Vista, which was founded in Sonoma Valley in 1857 and is considered California’s first winery, was purchased by Burgundy wine giant Boisset Family Estates. Sonoma-based Vincraft Group acquired Gary Farrell Winery, a pioneering Russian River Valley producer. It’s only the second winery in the Vincraft stable; the company bought cult Pinot Noir producer Kosta Browne in 2009.