DD smells and washes away in the rain. The smell is almost like turkeys famous outdoor fish drying practices, most tourists remember the stench clearly, not a good honeymoon option as my buddy recalls vividly.

crikey!

Fish oil works good for rust-proofing old parts

I once had a 1980 210 that burned oil almost faster than I could pour it in. I should have installed an oil tank and invented a crank case oil injection system. It was my work commuter car and I had no plans of rebuilding the A15. Instead I built a oil filtration system in my garage and ran used oil till I sold it.
I had to run it on almost pure rubbing alcohol to get it to pass Washington State emissions.
The filter was just a 4 inch black PVC pipe 6 feet long. Took a bunch of toiletpaper rolls and removes the cardboard centers. Vasolined a 1" PVC pipe and shishcabobed a stack of them. Vasolined the 4 inch pipe and crammed them in. Reservoir on the top and one on the bottom. It took about two months on pouring oil through the top to see it at the bottom but I had useable oil. At least for my needs. I think I did mix 1 new quart to every 5 quarts of used.
Sold the car and the filter went to the dump.

well everyone hates old engine oil, its toxic!

however I use it to coat old engine parts,
bottom ends and steel items in the backyard
as well as tools but also good for surface rust
on many things even old car panels sitting around
to the elements, so think or your datsuns bits
and at least give them some old engine oil.