The turbo is not "pressurized" with oil when the engine runs, the oil basically just passes straight through to the pan. There's no reason you can't just have the oil flow straight to the pan to test what you want. 603's have the oil feed threaded into the block, not tapped off the filter housing with a banjo.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]