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In many cases when you clean out an engine with any "flush' it just washes away the sludge that has been attracted to, and blocked out, developing leaks in seals and gaskets. Any engine will get leaky with time. Sometimes it seems like the sludge is all that holds some engines together, lol. I used to own an 85 300zx and used the NAPA brand flush, CRC I think, and soon after it popped a hole in number 1. Don't know if that caused it, but the timing of it didn't put my mind at ease. It leaked like a sieve after to.