(Adds details from letter)
   NEW YORK, Jan 23 (Reuters) - Hedge fund manager David Einhorn, whose Greenlight Capital suffered its worst year ever in 2018, told investors on Wednesday he had made some changes to the fund's main portfolio, including selling Bayer , Mylan and Perrigo last year.
   Greenlight Capital also sold Apple , which had been previously reported, and the fund manager said he covered short positions in Core Laboratories and oil frackers.
   "We are looking forward to a new season," Einhorn said in a letter to investors on Wednesday that was seen by Reuters, after Greenlight's main fund lost 34 percent in 2018, making it the firm's worst year ever.
   Einhorn listed Brighthouse Financial , AerCap  , CONSOL CoalResources , General Motors , Green Brick Partners , Germany's Deutsche Pfandbriefbank  , as well as gold and Puerto Rico GO bonds as long positions, while he is shorting Assured Guaranty and Tesla .
   At Tesla, he expects a "shortage of demand," and that the third quarter was "as good as it gets" for the electric car maker, which "faces challenges in 2019."
  
   CFO TO LEAVE
   Einhorn said Harry Brandler, the hedge fund's chief financial officer, will leave the firm this month after 17 years. He did not immediately name a replacement for Brandler, saying only that he promoted people in the firm's operations and finance areas.
   He said he was reopening his funds to new investments, after years of turning them away.
   "At this point, we no longer believe there is risk of our assets growing too quickly (other than through improved performance), so for those interested in investing, the answer will now be 'yes'."
   The firm's assets had shrunk to $2.5 billion, from over $10 billion four years ago.
   Many investors were fed up with heavy losses and Einhorn said the firm has had "substantial redemptions."

(Reporting by Svea Herbst-Bayliss
Editing by Bernadette Baum)
((svea.herbst@thomsonreuters.com; +617 856 4331; Reuters
Messaging: svea.herbst.thomsonreuters.com@reuters.net)