Thanks everyone for all the great suggestions. Based on the fact that I am trying to protect existing metal that is not virgin, nor easily cleaned, my plan is to use a oily spray called CorrosionX HD (heavy duty). It seems similar to the second Eastwood product I linked to above. The reviews on amazon are very positive:
http://www.amazon.com/Corrosion-X-90104-Heavy-Duty-12oz/dp/B0009H1AMG/
It is a thicker version of this product, which also has good reviews:
http://www.amazon.com/CorrosionX-Lubricant-Penetrant-aerosol-90102/dp/B0009E1QWI/ref=cm_cr_pr_product_top
It is sold by both of the aircraft sites that 97SL320 mentioned above, which is where I learned of it. So thanks again for all the help.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).