Forgive me if I am teaching my granny to suck eggs but when we changed the impeller of our outboard, we were advised by the service centre who sold us the parts that we should also check the plate and replace it if it had score marks. Once again, sorry if you knew that!
Haven't changed the oil ourselves yet so can't help on that one!
Edit: our engine is a Yammie - not sure if the impeller housing is the same on the Merc.
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