I put in my car a month ago,a used AEB engine. The engine is not in bad condition. Everthing stock, so I put new oil and start driving.
After 2000 km I was check my oil, and it was at same level, I must mention the engine was working perfectly... All of a sudden a few days ago, I get a rought idle, the car was idling at 700 rpm or lower, and i noticed a blue smoke and oil smell from exhaust. When I was driving i didn't noticed any problem or anything unusual.
That was trip of about 40 km and the problem with idle was there all time.  After that I checked my oil and there was a slight difference in oil level, beraly visible,maybe 0.5dl less.   
The nex day,and all days after that, car again work perfectly. Idle is normal and there is no blue smoke    I can't figure out what hapen that day, what could cause that.
Does anyone have any idea?  Thank you

I don't have Oil catch can, I have only this conected before turbo
https://www.carid.com/ic/wp/kayser/w01331736599kay_1.jpg
and it goes to crankcase

Like this
temporary image upload

Maybe, look this I remove the hose after turbo and there was oil in it. So definitly turbo oil seals are not doing their job.