As far as I can tell, POR15 seems like the solution to problems like this, both preventatively and as a repair. I haven't tried it yet, but I just got the starter kit in the mail, and it seems to be the right combination attack, a degreaser to clean, an acid to convert the rust to black oxide and deposit zinc, and a moisture-curing urethane paint to protect the rusted area and 'suck' the moisture out of the rust, preventing further oxidation. A fairly complete sounding one-two punch from a reputable company.

I suppose I'll be seeing soon how well it works, but it seems very popular for battery trays and the like.

peace,
sam

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"That f***in' biodiesel is makin' me hungry."

1982 300TD Astral Silver w/ 250k (BIO BNZ)
2001 Aprilia SR50 Corsa Red w/ 5.5k (>100 MPG)