Yeah, it's hard to tell (for me) how much damage your case has suffered by looking at the photo.
It does look (to my old eyes) like there's still plenty of the retaining nut left but there could be fractures in it that can't be seen because of all the violent contact that was taking place.
If it did "Kit-Kat" (you know, "break me off a piece")
or backed out on you it would probably be ccimplete disaster and a tow back to port.
I
can say that I
definitely would
not buy or install the unit in the ebay photo. That inner shaft support with the chunks broken out of it is a.deal killer for me. Both of the water seals press in at that location and they aren't there. I suspect that the damage may have been done removing them. I believe they would leak because of the damage if replaced. Running that case would probably be a bigger gamble than running the one you have. You can see the end of the needle bearing that supports the shaft in the photo and you can see that the damage to the support goes right up to it. A leak path right up to the inside of the case.
The difference would be that, if you tried the ebay one, you would likely know very quickly if it was no good after a run by draining the gear oil and finding the water I predict will be in there.
The one you have on there now might run forever as it is. Or, it could go several trips then
BANG, just let go.
Anyway, just my opinion and you've already seen it's often flawed.
But hey! I'll offer you just a bit more, even such as it is...
The 50hp Honda has been one of the biggest successes for them in their history. If it runs great, it's probably worth the effort and money to find a better lower unit and gain that piece of mind you spoke of. Great outboards those and LOTS of them out there.
You might try calling Tim's Outboard Repair In Hackensack, MN.
218-682-2331 to see if they have one to sell.
Others here have bought parts from them and have reported back with good experiences.
And don't forget, your transmission is still good so you might get by finding a good empty case and using your internals.
However, I urge you to buy and read the Honda Shop Manual before attempting doing something like that.
Available from them here:
The Honda BF35A, BF40A, BF45A, BF50A Marine Outboard Shop Manual covers service and repair procedures for the BF35A, BF40A, BF45A, and BF50A marine engines. See FAQs for assistance in locating your frame serial number.
publications.powerequipment.honda.com
Don't waste your $$ on Seloc or Haynes or other knockoff manuals.
1/2 price equals less than half of what you're looking for.
Good luck.
