The failing rectifier had smoke and flames coming out of it, so most likely it was shorting out. A lot of electrolytics were known to explode when a rectifier failed that way. They get really steamed when they have to carry high AC current. :)
I have replaced full wave selenium rectifiers with full wave silicon bridge rectifiers when they had marginal output to start with. You gained a couple volts on a 12 volt supply which was fine, since the equipment was designed to run in a car or truck. Like the little Sony
4" TV's built in the early to mid '60s. The last one of those I had with the original rectifier went up in flames while I was watching the TV. I was sick, in bed and had just woke as they announced Regan being shot when the flames started pouring through the vents in the steel case. Luckily, there were no screws in the case, and I managed to remove it before it burnt off the paint. :)