Thank you all for the suggestions. It sounds like it's inevitable that gelling will occur occasionally, as there are too many things not in my control. I chose the optilube after reading about all the different additives, but it seems each one has people who swear by it. Maybe I'll try the Power Service next time.
I will definitely try a different gas station and I'll buy some extra filters to have around. I still don't really understand why the filter gelled, but nothing else did.
My garage definitely never gets below the mid 40's, and that would be really unusual. I keep my jug of diesel fuel in the garage and it's fine.
I guess I'll buy some extra filters to have around.
What do you guys think of the black pitting on the walls of the fuel tank? I know the pictures weren't great, but it doesn't seem like it's related to the gelling problem. I will ask the dealer to look at it since it's well under a year old still.