Plus one on the above regards Original seal.
Not sure about the one in post above as see no guide.
OEM seal that comes with a plastic guide to get it in place correctly, also OEM gasket for housing that has pre applied sealer on it.
Fitting, The seal is a ptfe type and must be fitted dry, no oil on crank land.
I like to fit the seal into housing on the bench before fitting housing on to engine [ others are happy to do the other way around.]
The last seal I did was stubborn to go in and rather than risk distorting it put it in freezer for an hour to shrink after that it went in fine.
Trailerfitters tool box video on the you tube is useful info.
It is a lot of time and work to do this job again so doing it first time is good. Hope this helps. Good luck.
PS A friend had his 300tdi out three times before he got it right! But then the 300's seal housing is a pita of a design.