First time post here, but I think I should add my bit as I too have had Garratt issues. My Garratt died whilst under dc control. The forward unit ceased to work.
I made the mistake of returning the loco to Hattons (at considerable expense as I am overseas). The replacement they sent was in very poor cosmetic condition (bent valve gear, broken steps, broken foot plate). I haven't attempted to run it as I am debating repairing it or going through the expense of returning it again. I have emailed Hattons, and eagerly await how they are going to resolve the issue.
