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The set of symptoms described here, and in other posts, leads me to believe that there are several things going on here and that a simple cleaning of the venting system is not enough to solve this problem.
These 850 engines, and several others, seem suseptable to sludging--the accumulation of internal engine deposits. I suspect the reasons for this sludging are 1) poor maintenance (extended miles between oil changes) and 2) a high level of short-drive usage (where trips are short enough that the oil never gets up to full temperature for any extended period of time).
When sludging occurs, the venting system gets gunked-up with deposits AND the rings get gunked up with deposits to the point that they stick (no longer provide enough radial force to seal). The most suseptable ring is the oil control ring and when it starts sticking, it allow oil the pass in to the combustion chamber and burn. This is especially evident in high vacuum conditions, like when you are starting-out from a dead stop.
Additionally, any sticking of the compression rings causes blow-by and an associated increase in crankcase pressures. This increase in crankcase pressure causes the familiar leakage around the oil filler cap, the dipstick tube and, ultimately, the rear main seal.
So, it is possible to resolve these symptoms with a simple cleaning of the venting system. I would, however, put very high on the list the need to do a strong engine flush to free-up possible stuck rings.
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