I have not read the 473 posts in this thread so please excuse me if some of what I write has already been posted. I am not a pilot but my experience with jet engine oils may be helpful. I worked for 38 years with a major manufacturer of synthetic lubricants and have formulated and sold jet engine oils meeting MIL-PRF 23699, MIL-PRF 7808, and AS5780.
As I assume has been discussed here, a main suspect in cabin air sickness is TCP, which is contained in virtually all of the above spec oils at a 2-3% level. This additive is for anti-wear and ferrous metal inhibition. The balance of these oils is ~94-96% synthetic polyol ester, 2-3% amine type anti-oxidants, and small amounts of yellow metal inhibitors, anti-foam, and other additives. The toxic component in TCP is the ortho isomer, which is a potent neurotoxin. This isomer has cause oral poisonings in the past when levels were high, but the ortho isomer level has since been reduced to very low levels that the manufacturers consider safe. Toxicity is not my area of expertise so I cannot comment on its safety.
The polyol esters used as the base oils in these products are made by reacting neopentyl polyol alcohols with a mixture of short chain fatty acids from C5 to C10. It is the C5 fatty acid that contributes the "dirty sock" smell when the ester breaks down. This smell is not related to the TCP, but its presence may be an indication that the oil is a contributor to the odor.
If the cabin air sickness is caused by the TCP it is not an easy fix. Reformulating a jet engine oil to remove a vital additive is a task that costs millions of dollars and takes about 10 years to gain full approvals. Perhaps a faster approach would be to completely remove the ortho isomer from the TCP, assuming it is the only significant culprit. I'm not sure how practical this would be, but it seems easier than reformulating. Another approach would be a mechanical redesign to prevent oil vapors from entering the cabin, or a filter/scrubber to remove the vapors upon entry. Just speculating here since I was not involved in TCP manufacture and am not a mechanical engineer.
Happy to answer any questions about jet engine oils.