Man am I glad you posted this! It made me realize I forgot to seal mine when I installed and aligned my doors recently. What I do is, once I get the doors aligned where I want them, I take the bolts out and wrap the base of the threads with 3M butyl strip caulk and reinstall (one by one as to not lose the door alignment). Some of it squeezes out, which tells me they're all filled and sealed. Not sure what the factory used though.
