I had one of those "oh s##t" moments recently.
The main seal in the Le Mans had been weeping for a few months so I finally bit the bullet one weekend and pulled the engine out.
Imagine my surprise when I pulled the sump off to discover a good layer of mayo in there. The only saving grace was that it was too thick to go through the oil strainer. Took a few years off I can tell you. My hair would have gone white except my kids did that to me years ago

Now it hadn't that long since the last service so this was a fairly recent event.
Needless to say I flushed out the breather system and it was completely jam packed with thick chunky snot

Mike