Cracked TV175 S.3 engine case

I must have the worst luck with engine cases. One of the cases on my wife's Vespa VSC was cracked at a critical point -- a seal. It would be very risky to save the case. She now has good cases, but the numbers don't match. I am now have a TV175 s.3 case with a crack in it. I need to figure out what to with this case. Click on any photo to enlarge to zoom in on the crack.I have no idea if this case was cracked in the move. I doubt it as we were so careful with it. And it was stored in a rubbermaid wrapped tightly in old clothes. I will see if I have any close-up photos of this engine from back in PA to determine if I am the one that cracked it or not.
I don't know if the cases for Lambrettas must match in order to secure a seal and correct compression. It's my novice understanding that the Li 125 & 15o share this same case as the TV175 and the difference is the other case which is stamped. If so, maybe for less money that a TIG weld I could purchase a new case.
If not, I will need a weld. I suspect a TIG weld is the best choice. Either way I will research this and report on what I find.
My father-in-law is a professional welder and knows TIG. If that's my best option than I may ask him to do the work for me at a family discount.
I suspect a TIG weld and a proper grind down could be done for under $100.
The final question I have is . . . is the crack at a non-critical point and can this case be saved?
Please post a comment and make recommendations if you can. I will email my mentors on this issue and post their recommended solutions.

Since this post I have learned:

1) I can purchase an NOS case around $100. Or used for less.

2) Mike Analt from LCUSA wrote:
"That's an easy fix and a common problem. What happens is the front sprocket is either not tightend down when the cover is put on or the sprocket bolt comes loose while running. It dosen't look like it was running when it happend.

Any good alloy welded can fix it, usually around 50 bucks.

When you have it welded be sure to check the crack to make sure it dosen't leak. Lay the case cover inside up and fill the repaired area with solvent (carb cleaner works too). If the weld is bad it will leak, if it's good it won't.  the only thing the case cover does is hold the oil in the case and hold the clutch arm (so it works)."

3) My mentor Christopher Markley wrote:

"Yeah, JB Weld would do. Clean her up really well inside, JB it, and presto.
If you have it welded, consider that it will likely warp the part a bit, and it would be wise to lap it on a nice granite kitchen countertop or thick piece of plate glass. Then, just make sure to use something like Yamabond when you put it together, for extra sealing protection. Plus it's nice to see an old part stay on the road."

4) Tom G. wrote:

"Jeremy, Don't sweat this too much. Its just a chaincase cover, so only that has to be replaced (or repaired). The main case component is the rare and expensive one. The chaincase covers are interchangeable between all Li models.  As somone already posted on your blog, all this cover has to do is not leak oil. You can epoxy it, weld it, whatever. Or replace it for about $35."

5) Stu Werner wrote:

"Buy a new one."

I have decided to have mine welded by a local LCUSA member and will post a follow-up after I have it done.