if you suspect that the oil pan has already accumulated so much deposits, then why not remove the oil pan and clean it manually.

as for engine flush, tama sabi nila. put that in your engine and you can say goodbye to it. it's mostly kerosene loaded with a lot of detergents. would you mix kerosene with your engine oil? i don't think so di ba. so if you really need to flush, correct na naman sila! use oil!

don't use any of those oil additives either (ptfe, slick, etc.). gastos lang yan and it will just kill your engine in the long run.