Call Dexter with the numbers--they have a very detailed list of everything they supplied to trailer mfgs.
I think the website is www.dexteraxle.com
Leading/trailing is only a reference to where they were placed, should not be difference in axles. I would not obsess over these items, just the bearings and brakes.
You DON'T have the NevRLubes, I would bet, and if there isn't a grease zerk in the center of the hub, then you don't have the EZLubers either. Probably just the normal hand-packed bearings. Take it to an axle/spring shop and they can inspect the bearing and repack them, or you can do it yourself if you are handy at things like that.
As to checking the magnets--jack each wheel up and apply the brake while someone trys to rotate the wheel, that should tell you if it is working. Don't jack on the axle, use the spring mount plate to place the jack.