TCM SIL99-2B might provide some guidance:

ADDITIVES

There are many fuel and oil additives and/or concentrates on the market today which were formulated primarily for automotive and industrial engine applications. From time to time, we receive inquiries as to the use of these products in our aircraft engines. Most of these additives and concentrates […] are not compatible with air-cooled, light aircraft engines in their operating environments […] we do not recommend the use of additives or concentrates in any of our aircraft engines. In fact, the use of such can be cause for voiding the warranty […]