ahdofu

I am in the process of replacing the bearings on my OS engine. Having removed both bearings, I see that the rear one is shielded on both sides and the front one is shielded on one side. What is the recommended procedure with rear bearings? The new one that I have is shielded on both sides. Do I need to remove both shields or should I use it as is since the OS also used a shielded rear bearing? The replacement front bearing has rubber shields on both sides and the manufacturer recommends that they both stay on..
Matt