40 ho mercury gear oil

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Feb 3, 2011
Golden Meadow, LA
i just serviced the lower unit in my cousins 40 hp mercury, 2004 year model. It still had the original oil, 10 years old and pretty nasty. I used Lucas M8, is it any good? Im not a fan of any Lucas roducts, from what ive read on here, but i figured id give the gear oil a try.
I can only relate my experience with Lucas gear oil. Bought some on sale and put it in my transfer case(toyota tacoma). Within just a few months it started leaking from the front seal. I pulled the top plug and inspected it, it was very dark and nasty looking. Switched it out for some Mobil1 75w-90. It stopped the leak, and remains looking good after years in service; never again. My suggestion would be to change it out as soon as possible.
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