I looked at my 603 engine and I agree that GP #3 and #4 look extremly hard to replace and I would agree to put new GP in those two ` if the intake manifold was off. However, I still would not replace any of the other 4 untill they failed. I would keep the 2 from #3 and #4 for spares.
Good idea about the GP relay fuse. They are so inexpensive from Fastlane that it doesn't cost much to carry a spare. I have never needed a GP relay fuse in 11 years and 170,000 miles but I still do carry a spare. I also carry a spare GP or 2.
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