I remember that when these units first came out, I was working for a Cat dealer at the time. There isn't a replaceable seal at the back of the crankshaft.
Peugeots are noted for leaking head gaskets and if you weren't careful removing the head, the liners would break loose and cause a lot more problems. I found that the breathers, hoses, and oil filler tube had a nice yellow foam coating plugging the openings. I guess they were preventing the PCV system from working properly and building up internal pressure which is causing the oil leaks.

Now try and get a Peugeot to start and run properly....................that's another can of worms.