I think 5/30 is too thin too. Personaly I use 15/40 in all of my engines that have flat tappet cams, like your 235. The big oil companys have droped the amount of zinc and phosperous in motor oil for years because of new car emissions. It has reached the point where cam manufactures have seen an increase in cam failures. This probally won't happen to you but why take the chance with these oils that are taylored to the newer cars. 15/40 has all the good stuff older engines need. I would change the pump and not do anything to thin the oil. With the pan off you'll have a chance to clean it and the pick up screen. Hope this helps.

Sean

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