Not sure about the 20 but the 300 for sure does not lubricate the rear output bearing when it is being towed. That TC uses the spinning of the mainshaft to fling and lubricate the bearing, so when it is in neutral being towed you are not getting any lubrication. As long as its short distances not a problem, but if you go any distance you need to do something about it.
One thing is to stop every 50 miles or so and drive it around to lube the bearing, but I think it is much easier to just remove the drive line. Thats what I always did. It takes 10 minutes if you are slow. 8 little bolts and you can just pop it out and go. This is the best way.
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