FWIW have done 3 hydros to date and all have been successful.
The cost to the customer was almost the same as the retail price of a replacement tranny so they ended up saving about $ 200 but only have my warranty on my repair.
If they went with a new unit then they get 1 or 2 year warranty.
I did them because I have never done one before or in the case of the Murray because the tranny is no longer available.
I do them in the bathroom of the house that I work out of after wetting the walls & floor with a hand shower then wear a pair of painters disposable coveralls with hood and also wear long nitrile gloves.
There are a lot of videos of people pulling them down on their garage floors and they always seem to be successful, but what you don't get shown in the units fail 2 years latter.
There was even one video where the "mechanic" was rabbiting on about keeping stuff clean & he had fingernails with enough dirt under them to grow potatoes.
The ones I did were power washed then soda blasted before I split them to get rid of all of the corrosion on the outside.
A very small amount of dust will kill then quick smart.
They are really not meant to be fixed.
The motor pump units for the T40 I have just replaced was $ 680 and there is 6 hours in doing the job = $ 1040 + freight
The complete unit was $ 1100 + $ 120 for fitting.
If I could get a unit from www.mulliganspartscompany.com it would have been cheaper to replace the box as a unit.
I can't speak for other brands, but Hydrogear only has a 90 day warranty on replacement units installed by an authorized hydrogear service center. If the customer buys it and installs it himself there is NO warranty.