It isn't a lot of work to do it yourself. The ODGuru who posted above has done many. I have done three, and am working on the fourth. ODGuru had done many. The ODGuru also sells the o-rings if you don't have a local source.

There is lots of good information in the 700/900 FAQ. Be sure to stall the engine out with the transmission in reverse to help get the OD off of the splined shaft. Once you have removed the eight 11mm nuts (they are probably 7/16"), the OD can be worked off the transmission. The picture below shows what you will be looking at then. The OD pistons are under the two bars.



You don't need to overfill the M46, but if you had an M47 you should overfill it. The M47 fills to a lower level in what is the same case as an M46. Overfilling an M47 will bring the fluid up to about what is usually in an M46.