What kind of temperatures are you reaching with your oil just before the IP? Have you checked for any air leaks? If you have not you should install some clear tubing before the IP and check for air bubbles in the system.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine