Wow. Great job. I get so embarrassed at how I wailed and gnashed my teeth on my thread about all the "terrible rust" I had to deal with, when I see what you guys have to deal with ito rust.
I nearly ran away when I saw all the muck lying in my frame. (It was right to the top of the cut outs.) At first sight I thought the frame must be a goner for sure. Fortunately for me no harm had been done other than a bit of really minor pitting. It seems to me that this is a common problem as there is just no way for water etc to drain out of the frame other than seeping out slowly through the seams, and obviously has plenty time to deposit really solid layers of sediment.
I did think of drilling two 1/2 " drain holes at both ends of the flat part to speed up draining, but for some reason I didn't do it. I really regret that now. The next one will definitely get that.
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where I got really lucky on this was that there was a lot of diesel mixed in with all the muck which must have offered some protection.