All three of our 850s had some oil on top of them, one had a LOT.

I cleaned them off and always used a rag to guard against spills when adding oil.

I even checked the top of the engine after oil changes - once, the technician did spill some oil.

They did stay clean for the 10 or 11 years that we owned the cars.

I did check the filler cap gaskets once and a while - I think I changed them every three years or so.

On one car, I bent the ears on the oil filler cap so that it would fit snugly.