Have you tried the basics? Is the monitor on original capacitors? Start with a cap kit. I believe that it is also possible to source replacement Chinese flybacks for this model, so consider changing that as well. If you decide to do a cap kit, take note that there are a handful of bipolar caps on this chassis, so make sure you don't miss those. There are also may be some oddball large bipolars that can't easily be sourced, so maybe just leave those alone.
You say you keep it in a very cold garage... have you tried heating up the garage and letting the monitor warm up for 30 minutes? CRTs have a warm up time before they are at normal operating brightness.
