Best way to install the rear main seal on a 5.9 magnum

Hey guys over the years I've installed several rear main seals on my magnum engines and some have leaked which is annoying on a brand new engine. I used to just put Loctite in the groove and then press the seal in but this has leaked several times for me.
The last one I did I placed a generous amount of gasket sealant in the groove and then press the seal in and it didn't leak. Don't know if I got lucky or this is the correct way to do it.
Could someone please confirm the best way they have found.
I have noticed in the kit there is a little white funny shaped piece of plastic. Not sure if this is to be used to spread the sealant.

The little plastic piece is to be used as a type of shoe horn for putting the seal in so the edges don't get cut. (I don't use it)
Rear main seals never used to come with them, so...
I just oil up the seal and slide it into place only using a dab of RTV on the ends where the two halves meet.