I just used two screwdrivers to press it in and had a helper remove the lock ring. Without a helper it would be impossible obviously.
Make sure you get the seal the right way around for inner pump and use non-hardening sealant on the pump bolts.

Some photo's here:
http://w124-zone.com/articles.php?article_id=21
follow the manuals, use both in unison side-by-side.
http://www.w124-zone.com/downloads/photos/300TE/remove_tranny/tranny_722_repair.pdf
http://www.w124-zone.com/downloads/photos/300TE/remove_tranny/transmission%20repair.pdf

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k