just a word of caution from a past experience. i had a car that was well maintained and it was bought brand new. decided to try one of those engine flushes and it worked great. the only problem i had was that it loosened so much crap that i wound up having to drop the oil pan and remove the oil pump to clean it and the suction screen out.
if the engine flush was done from the start it probably wouldn't have had that happen but who would have thought as the oil and things were maintained properly.
i know of one place near me that won't do a tranny fluid change on cars that have high mileage and never had it done before. as they are not a tranny shop they had too many experiences with doing them and the new fluid (which has very good cleaning properties) would loosen all the contaminants and then the tranny would start slipping. when a customer with that high mileage and no service would want it done they would refer them to a tranny place and explain why.
may want to try a little bit at a time if you never had this done before.
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THE DYNAMIC DUO