I pulled my air cleaner off and noticed a small pool of engine oil in the intake manifold, vacuum pump?
Thanks

Just trace what ever tubes go into the Air Filter Housing back to their source.

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84 300D, 82 Volvo 244Gl Diesel

Just to sort it out - pull the crankcase breather hose off the air cleaner and run it to a collection can. You can drive that way for a while (maybe 1,000 miles or some such). See if your air cleaner still gets grubby. If not, you're looking at blowby - check your temporary breather can for evidence.

Because I run a cone filter right off the turbo (I know, you don't have one of those) I didn't have anywhere to vent the crankcase so I have a racecar type breather can (commercially available) with both the crankcase and the valve cover breather run to it. So far I have had NO blow-by accumulate in the can but of course there could be. I'm thinking my engine has really good ring seal.

Dan