The hunt for information on W T Murray began with the story of the Avondale Supply Depot, continued through some Googling, the account of his death on Mt Egmont/Taranaki, and contact with the historian for Clan Murray, and then on to the story of Highlander Condensed Milk. I left that last part with the question: was the W. T. Murray of the dairy company which developed the Highlander brand the same William Tullibardine Murray I had been chasing?
As a William Tullibardine Murray of Auckland (formerly of Wallacetown in Southland) was among the list of those selling the patent for "Murray's Concentrated Milk" to the new company of W. T. Murray & Co in 1898 -- it looks like the answer is yes.
On 21 March 1898, Murray, along with Henry Norman Bell (manager), Henry Burton (gentleman), Frank Jagger (merchant), William Alexander Mercer (gentleman), James Macfarlane (merchant), Frank Duthie (gentleman) and Charles Vince Houghton (manager) set up the firm W. T. Murray & Co, conveying the patent rights, "together with buildings, plant and machiney" to the new company. In 1892, their previous company had been located at the frezing works wharf in Auckland; by June 1903 they had relocated their registered office to Esk Street in Invercargill, and in 1906 they were in Spey Street in the same city.
William T. Murray was a shareholder of the company at least until 1901 and 1902, both years referred to on the shareholders list as living in Toowoomba, Queensland, as a manufacturer. He ceased to be a director by July 1902, and that is the last year he held shares in the firm which maintained his name until 1918, when it became New Zealand Milk Products Limited. In 1924, Nestlé bought them out.
Source: Closed company file on "The New Zealand Milk Products Ltd (ex W T Murray and Company Ltd, Murray's Ltd), BADZ/5181/67/459/1898/3, Archives New Zealand, Auckland