First time I have ever seen a broken diff
Easy drop in parts but check the cylinder chest on both the pump & motor for gouges made by the shrapnel.
If the magnets have been ding their job it should be fine.
Otherwise Mulligans seem to be the best people for tranny parts
Thanks for the links MM. I was able to order a differential repair kit for about $35 with shipping. I've got some Loctite Superflex Red RTV gasket maker that I think should work ok, so I could get out of this fairly cheaply. Most threads and videos I've found on K46/T40 suggest using 5w50, so that'll be another $30 or so in oil. Altogether, not too bad if I can do it right.
To get me by I rolled the dice and got a used unit on ebay for $170. I drained the oil (which actually looked pretty good) and cleaned the magnet (which also looked pretty clean). I don't know if it was spruced up for sale, but it appeared to be in great shape. I put some fresh 5w50 in, purged the air with a drill, and slapped in it. So far so good! So if I can repair my old one I'll have a spare for my mower and my brother's (his LA115 also uses the T40). I can tow my aerator and dethatcher with slightly less stress, lol.
When I service a fully sealed tranny and do not change the pump / motor unit ( down here they are $ 800 - $ 1000 , about 1/2 the new box price ) I went up to the next highest base viscosity
So I would advise to go to 10W 50 for your old box .
When they get old & start to slip I used to tip the old oil out & go one thicker
I can do it down here in OZ cause it dos not snow so no need for very low viscosity oil
Old leaky ( intenally ) K46 can run for quite a while when upped from the 10W 40 JD uses to 20W 50 .
If yu fit a new pump / motor then use the original specified grade as there is no wear to compensate for.
A few years ago a back yard machins shop started refurbishing Hydros so I no longer touch them
HE charges about 1/2 the parts price to machine the cylinder block & valve plate back to the original surface finish.
What I find amazing is no one does the same thing over there.
What has happened to the "land of oppertunity "