I've never brazed before but I may give it a try here. Someone has been at it before. It seeps some for sure. I want to fix it or possibly replace if I have to but I'd rather repair if I have a decent chance at a reliable fix. I'm planning on removing pony. It has considerable main bearing movement and leaks oil like a sieve. Will pull it all apart and make sure nothing is on the verge of scattering. Do I have a good shot at making a decent repair on this? Anyone? Ideas?

Very common to find brazing repair on those pony motors. Casting is thin to begin with, freezing takes its toll. Usually the worst on the bottom of the cylinder block.

On the positive side, those lousy mounting nuts will be easier to remove since they have been nicely soaked in oil, don't forget the one hiding down between the pilot and main motor!

Have seen many repairs far worse than that braze repair that lasted a life time. May be able to find the small spot that weeps and do just that spot. If just a pin hole or void in the original Braze could just solder that spot. Pretty is not important. Bob

You could just cleaning the poney first and start it if he is leaking only by the crank shaft seal and have bad front bearing and if he is't leaking were he ben brazed you could just removed the flywell.and removed the rear cover and changed the seal and bearing if the crankshaft have no damage

Good Idea - Clean pressurize the radiator and may find just a small coolant leak easily fixed in place. Then pull flywheel and cover for bearing and seal - easier than pulling the pony. Bob

I’ve also had pretty good luck patching a brazed repair with JB weld. Just have to get it clean and dry

It looks like the past repair was done in place. When soldering or brazing cleanness
is required. Just saying proper prep work is the key to a successful job, more so than experience. Grab some old metal and a how to book and practice. I am a chicken when talking about welding gas tanks so when the pony engine tank developed a leak I drilled and tapped a 1/8" pipe plug hole and installed a plug. For an in-place repair this would work on a small hole. If I were pulling the engine anyway I would remove the patch, clean it up with a grinder, finish it up with a file to re-open the pores and re braze it.

I would suggest you use expoxy. I have done a bit gas welding over the years,some times it looks like I know what I am doing. Other times you know I cannot. My guess looking at your pictures is not clean enough and/or enough flux.

Gas welding is a lost art with all the cheap migs to do light sheet metal.So I don't want to discourage you but cast iron that has to hold liquid is not a good starting place.