When I use Engine Flush before adding new motor oil to my engine, will this affect my engine’s seals in a negative way, as some oil flushing products are know to do?

No it will not affect your engine’s seals. The reason our Engine Flush does not embrittle your engine’s seals is because our product is based on oil, and not on a solvent as some competing products. Solvents can be corrosive and tend to affect rubber parts. Our Engine Flush is oil based so it’s not corrosive in any way and is compatible with all mineral, semi-synthetic or full synthetic motor oil.