I think its just age, with the 617 pumps. Nothing lasts forever, and at 300k miles it might not be a bad idea to put a new one on.

The 603 pumps were just a bad design, the new ones don't seem to fail.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200