The Mengelberg-Kaplan manuscript of the Second Symphony is being sold by Sotheby's tomorrow in London. This is the original of the Kaplan facsimile that most will know of. According to a Sotheby's spokesman today on BBC Radio 3 said the last Mahler symphony manuscript was sold in 1959 and is at Yale. Pre-sale estimates are ₤2,500,000 to ₤3,500,000 (approximately $3,125,000 to $3,375,00). Alma gave it to Mengelberg and Kaplan bought it from the Mengelberg Foundation in, I believe, 1978.
Of course, Mahler made further changes, but the manuscript even in facsimile is very impressive.
Tom in Vermont