That's an interesting fix. I'd like to read about it. No reason in the world why a good mechanic couldn't do that.
But doesn't it seem a little easier to just put a shielded vent in the top of the cover and a drain in the bottom? Then run them dry as designed.
Both vent & drain are basically quarter inch holes with an inch or so of downwards-pointing copper tubing inserted.
Just musing now.....that whole old Yanmar line all all suffer from water in the brakes - the JD1050 is basically a re-badged Yanmar...I think it was a Yanmar YM3810? And brakes that get water in them and rust just seems wrong for tractors made to be used in fish ponds & rice paddys.
I guess some things are better left a mystery. But if you vent and drain the cover - and quit driving around in ponds and rice paddys - your next set of brakes ought to last the life of the tractor.
Parts are available, and shoes can be re-shod if necessary. The brake drum has plenty of thickness to lathe a few times. All that's left is a couple of standard metric seals and two springs. Simple/dimple like apple pie...
You don't even have to lay under the tractor. Take off the rear wheel(s) and you can do the whole job sitting down.
Good luck,
rScotty