When asking a club member about how much to torque the rear axle nuts he said if it's tight it good. Then he asked if I had sealed the key way and key with RTV sealant. I asked why and he said it is to keep grease from the bearing from migrating down the key way and getting onto the drum. I thought about that a sec and replied that if any grease could work its way down the key it would come out the end of the axle and hub behind the nut and washer.
The only way I see grease getting into the drum is if the outer seal on the backing plate is damaged. Look at the illustration!
Maybe he has hubs that were drilled through to the key ways to make them lighter weight?
Pretty sure I'm getting hosed on this bit of info unless someone can prove otherwise.
If you will note the construction of the brake drum the key is cut completely through the length of the hub. If no sealant is used ( as someone wisely advised ) grease can work it's way along the key and into the brake drum. I've been told on several occasions that this advice is "hokum" but believe me it's absolutely true and besides, who has anything to gain by suggesting the use of a little RTV on the key way and tapered portion of the axle? My source is the master Chrysler mechanics I worked with and knew many years ago - not my own ' wisdom'.
Some cars may have a rigid felt seal behind the axle nut / washer to seal the end. A Model A Ford axle seal could be adapted.
My impression always has been that such felt washers are dust seals. One placed in that orientation will not prevent lubricant from entering the brake drum.