Just thought I would pop back with an update in case anyone else ever has a similar problem. Decided not to try a professional dye job as it sounds rather risky so I got some Cherry Blossom Premium Renovating Cream in Lipstick Red and did a test run on the padlock fob thingy which seemed to go OK. The I applied the cream all over the bag carefully with a fingertip as it seemed to give more control than the recommended 'use a cloth' method. I left it to dry a while and then with a soft cloth I very, very lightly buffed the ostrich leather in the direction of the quills. Then I repeated the process again. I'm rather pleased with the result. It still isn't a proper bright red - it's now more terracotta rather than the faded coral but it looks much more nourished and has lost that dry, slightly chalky look. Also the patchiness is improved - the colour is much more even. I might even do it once more before giving it a Collonil waterproofing spray. I'm just so pleased that I haven't ended up ruining the bag!