I don't know of any kits available. I've always procured the parts individually. The usual culprit for oil leaks is the open bearing at the output end. This should be replaced with a sealed bearing. There are arguments for and against removing the inner seal. I always remove it.
You need to follow the appropriate service sheets or maintenance manual and there are tip in the technical page.
A statement like that isn't much use to anybody really....If you have new information that you think is useful it would be better to share that here for some discussion of its merits and some comment from other forum members who also have experience of the job...Personally I've modified the way I do things a number of times following posts from other members, particularly one Dutch contributor who frequently comes up with a different idea...
That is the purpose of a forum after all...Ian