He shows up if you do an advanced book search (full view) at Google Book Search in a number of documents (Primarily Hart's Army List. The last entry for him, in 1855,in United Services Magazine, Part 1, p. 502 shows him going from half-pay to Staff Surgeon of the First Class (a rank which he had apparently held previously). In 1846 Hart's it shows that he had 27 years service at full pay and 4 months at half pay, which means he joined c. 1819. Very unlikely to have served in the Crimea at his age. I found an obituary for a Dr. Alexander Sinclair in Gentleman's Magazine (Jan-June 1864)p. 265; he died December 26, 1863 at Southsea.