You may be referring to these articles, but these articles have many errors and incorrect assumptions, such as misunderstanding the difference between "clearances" and "tolerances."
https://www.aopa.org/news-and-media/all-news/1996/january/pilot/airframe-and-powerplant
The problem with the Mobil 1 aero oil was not the full synthetic base oil mix, but the additive chemistry. The additive chemistry did not properly scavenge and disperse lead deposits.
"..Mobil introduced its 100% synthetic AV-1 piston aircraft engine oil with great ballyhoo in connection with the 1986 round-the-world Voyager flight. It went on the market in 1987, after five years of R&D and 25,000 hours of flight testing in 23 different aircraft. Teledyne Continental enthusiastically approved AV-1 for use in all TCM engines with oil filters. It didn't take long before isolated cases of lead sludge accumulation became apparent in some (but certainly not all) engines using AV-1. Both John Frank of the
Cessna Pilots Association and yours truly started advising against the use of AV-1 in low-utilization owner-flown airplanes as early as 1991.
Our rationale was that 100% synthetic oil is a superb lubricant but a lousy cleanser, and that cleansing is extremely important in piston aircraft engines because of their loose tolerances and the significant blow-by that can leak past the rings and contaminate the oil. But while we suggested owners not use AV-1, we honestly didn't anticipate that the lead sludging problem could reach the severity revealed by the Gross and Eriksson teardowns..." Emphasis mine.
https://www.avweb.com/features/mobil-av-1-under-attack/
I think the bottom line is to use an oil with the proper additive chemistry for the intended application. The use of leaded fuel is an outlier to the norm. It is up to the user of leaded fuels to deal with the ramifications of such.