I'm usually ok on figuring these things out, but I am stumped. While cleaning and rejuvenating a Model 20 rear end for my buddy's CJ7. I noticed some strange things. According to the tag on the front Dana 30, it is a factory 4.10 setup. Verified by tooth count. When we removed the differential cover to check out the rear axle, the tooth count was verified as also 4.10. It also has Yukon one piece axles which is a good thing. Now, when I was inspecting the side gears, and the spiders, I noticed the pin was inside a "slotted" hole. Unfamiliar to me. When turning the pinion, both sides turn the same direction, indicating to me as being some sort of limited slip, or locker. I'm just baffled by the "slotted" hole in the carrier. Does anyone have any ideas? It doesn't look like any lunchbox locker I've seen. Thanks in advance for any ideas.