I would put some sealant on the bottom of the seal.

Another thing to check is to be sure that there aren't any rust holes in the bottom of the trough where the seal goes. Those would need to be sealed up. RTV would work for that as well as for the bottom of the seal.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.