There are 2 seals. One is on the cab and the other is on the top. The one on the top is probably the one you need. LMC, Year One have it and you can probably still get it at the dealer. It glues on. Need a high quality contact adhesive. I'm about to do the same. THe seal on the cab was in perfect condition on the Lady's 79 but the top seal was done. On ours it appears to be getting past that seal and then leaking over the rail into the truck and bypassing the inner seal all together.
Women dig dents and flat paint!
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Grim-Reaper