To prevent the oil filled (paint)can 'weeping' oil it is important that
the can's vertical and bottom seals are tight by applying solder inside.
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That hasn't been my experience, but if one must solder, for sure don't
use a lined can. And then after soldering, clean and apply a
protective coating on the outside to cover all areas where heat has
discolored the metal... because these areas will be far more prone to
rust.
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It is hardly possible that rust develops when the can is filled with
(any) oil.
Another way to prevent oil weeping from the can is to cover the seams
internally with 2 component-expoxy adhesive.I had a motor oil filled
dummy load in operation for 15 years without problems , resistance
measured remained constant (50.3 Ohms) over that period.
That dummy load was made with 20 ea 1000 Ohms ,2Watt carbon film
resistors. With so many resistors in parallel the inductance of the
device is sufficiently low for use up to VHF frequencies.

Frank GM0CSZ / KN6WH