This has been discussed here many times. It doesn't hurt anything. Likely
does lube the pump. Doesn't seem necessary according to most. I used it
for a while when I first got the car but after reading here for a while I figured it was something I could live without. There was one I read about
called Opti-Lube ( don't quote me on that ) that really did do a great deal
but it was a bit expensive. Most folks here with high mileage cars got there with no additives.

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85 300TD FED-Daily
84 300SD-Wife's
86 XJS-Sunday
66 GMC-Work- Given to my stepson
83 BMW Airhead- Given to my stepson