Originally Posted by Issac

This hearing design came out in the Late 80's if you can believe that. It's a little on the lower quality side I always felt but is very bomb proof.
I think your overthinking it.
The seals get too big. Harbor freight sells hundreds of o- rings for a few bucks.
The beauty of the bushing with an outside ball contained roller is that the bushing is also a type of seal because it's not a tight fit. Dura ace used a roller bearings in the middle and ball bearings both sides but Dura ace required a lot of work and this system you take the axle off by using the little plastic tool and squirt grease in the bottom of the pedal inside about half a ribbon of tooth paste and tighten back up. The good grease poops the bad grease out and you overhauled your pedal in one minute. I've rebuilt dozens of Brands of pedals, and they are a total pain to replace bearings. On the Shimano a 10mm wrench can adj. the roller if it's got play.
Bushings have no place on bicycles IMO, but on mountain bikes the pedal is great. If you trashed that o- ring and once a month squirted a little grease it last so long you'd be sick of SPD. Don't let a tiny seal bother you, as long as grease goes out now and then ... your set. Also performance has a $33 price on Shimano mtn. Double sided without the pathetic seal issue. O-ring. But if you want to get perfectionist ( good god they are mountain bikes) like the man says drill and tap a zerk and grease guard it with synthetic- that's the stuff us road guys did which of course is justifiable!