Steinway Musical Instruments has been sold for about $499 million and will again become a private company. The Waltham-based piano maker struck a deal with Paulson & Co. for $40 per share, topping an earlier $35 per-share deal with Kohlberg & Co. It will discard that deal and pay a $6.7 million penalty. Steinway suffered during the recession. Sales have increased in recent years, but have yet to return to prerecession levels. The deal is expected to close in September.