I may be all wrong here but here are a couple thoughts.
I don't think the oil filter collapsing is a good sign. At the same time I don't see how that would cause oil to spew from the dipstick. It certainly could cause the light to come on if the flow is restricted.
I think the spewing problem is with the crankcase ventilation or overfull of oil.
You said the oil is where it is supposed to be on the stick but do you actually know the levels on the stick are correct from installing the correct amount and verifying the level with the dipstick. Has the dipstick or tube been replaced?
When you checked the vent hose did you just check the elbow or did you check the entire hose, including where it connects at each end? Is there oil build up in the air cleaner housing? That would indicate the hose was open at least.

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Darrell

1984 300SD "Ole Girl"
207K